P19.2: integration — refresh goldens for the merged organic motion + finalize docs

Final golden sweep + doc finalization for the organic-animation pass. No .sx
logic/render change; goldens + README only (CLAUDE.md is local-only/gitignored).

Refreshed 8 stale goldens to the SHIPPED render (each verified deterministic):
- p6_anim_swap/clear/fall, p6_fx, p6_inputlock_board (M3TE_FX=3 at swap/clear/fall
  segment phases): last captured at P13.1, so they still showed the PRE-organic
  flat tweens; now show the merged overshoot / pop-ripple / gravity-accel motion.
- p17_fall, p17_stagger, p17_land (M3TE_FX=11 deep cascade): captured incrementally
  at P17.1/.2/.3 and never updated as later steps changed the shared cascade frame
  (P17.2 stagger, P17.3 squash, P18.2 burst ripple), so the committed PNGs no longer
  matched the shipped code (12-20% board-region diff). Re-captured to the final,
  fully-merged fall motion at their documented phases.

README:
- Added the previously-undocumented move-timeline frame recipes (swap/clear/fall/
  after segment phases + the resting-board goldens), filling the doc gap.
- Fixed the now-false P17 prose: p17_fall was described as a "pre-stagger lockstep
  reference" and p17_stagger as carrying "no squash" — both untrue once the full
  fall motion shipped. Now describes all three as the final combined motion, each
  pinned to foreground a different tell (accel / staircase / squash wave).

Verified all 28 goldens: 8 refreshed, 20 unchanged (board+HUD region byte-identical
over a status-bar/home-indicator crop), 0 removed. t=0 rest, win/lose, HUD, select,
idle, FPS, p16/p18 and p11_combo_deep all reproduce. Gate green (ios-sim build +
22/22 logic tests; tests/gem_pose.sx + tests/easing.sx pin the t=0 rest invariant).

README.md

@@ -329,8 +329,7 @@ distance: in lockstep their gems share one height (a flat row); staggered, they
 form a diagonal. On seed 1337, `M3TE_FX=11` **round 4** refills columns 2–7 by one
 cell each (its fall window `[1.74, 1.96)` s); at `1.91` the leading column has just
 landed while the trailing column is still ~⅔ cell high, so the top row reads as a
-left-to-right staircase instead of a flat band (contrast `goldens/p17_fall.png`,
-which is pre-stagger lockstep):
+left-to-right staircase instead of a flat band:
 
 ```bash
 # Refilled row pouring in as a staggered cascade: goldens/p17_stagger.png
@@ -379,10 +378,15 @@ env SIMCTL_CHILD_M3TE_FX=11 SIMCTL_CHILD_M3TE_ANIM_TIME=3.0 \
     xcrun simctl launch --terminate-running-process booted co.swipelab.m3te
 ```
 
-`goldens/p17_fall.png` stays the pre-stagger lockstep reference (P17.1) and
-`goldens/p17_stagger.png` the pure per-column stagger (P17.2); both pin moments where
-no column has landed yet, so neither carries squash. The change is render-only — no
-`board.sx` model change, and a resting board is untouched.
+All three fall goldens were re-captured in P19.2 to the final, fully-merged fall
+motion (gravity accel + per-column stagger + landing squash), each pinned to
+foreground a different tell of it: `goldens/p17_fall.png` (round 3 at `1.51`) catches
+the columns bunched HIGH under the gravity accel before any has landed (so it carries
+no squash); `goldens/p17_stagger.png` (round 4 at `1.91`) catches the left-to-right
+staircase as the leading column just touches down; and this golden (round 4 at `1.94`)
+catches the squash wave once the leading columns have landed-and-flattened while the
+trailing ones still pour in. The change is render-only — no `board.sx` model change,
+and a resting board is untouched.
 
 ### Organic combine — anticipation pop on clear (P18.1)
 
@@ -496,6 +500,58 @@ env SIMCTL_CHILD_M3TE_FPS=1 SIMCTL_CHILD_M3TE_ANIM_TIME=0 \
 digits are dynamic, compare the FPS text's PRESENCE in the top-left corner, not its
 exact value. Every other golden is captured with `M3TE_FPS` unset and is unaffected.
 
+### Move-timeline frame goldens (P6.1 / P6.2)
+
+The board-motion timeline (`board_anim.sx`: swap slide → matched-gem clear →
+collapse/refill fall) and the match-FX layer (`board_fx.sx`) were first locked by a
+set of frame goldens captured off ONE committed move. They use the same `M3TE_FX`
+hook as the FX captures above — `M3TE_FX=3` is the seed-1337 vertical red 3-match (a
+single round) — each pinned with `M3TE_ANIM_TIME` to a phase of the swap→clear→fall→
+settled timeline. Re-captured in P19.2 so each now shows the **organic** motion merged
+in P16–P18 (swap overshoot, anticipation-pop clear ripple, gravity-accel fall); the
+canonical per-feature organic goldens live in the P16/P17/P18 sections above, and
+these are the generic timeline frames at their segment midpoints.
+
+```bash
+# Swap segment midpoint — the swapped gems caught PAST target (ease_out_back
+# overshoot): goldens/p6_anim_swap.png
+env SIMCTL_CHILD_M3TE_FX=3 SIMCTL_CHILD_M3TE_ANIM_TIME=0.08 \
+    xcrun simctl launch --terminate-running-process booted co.swipelab.m3te
+# Clear segment midpoint — matched gems mid pop-ripple, composed with the burst and
+# "+30" popup. The SAME committed-move frame backs all three of:
+#   goldens/p6_anim_clear.png == goldens/p6_fx.png == goldens/p6_inputlock_board.png
+env SIMCTL_CHILD_M3TE_FX=3 SIMCTL_CHILD_M3TE_ANIM_TIME=0.23 \
+    xcrun simctl launch --terminate-running-process booted co.swipelab.m3te
+# Fall segment midpoint — the refilled column caught bunched high under gravity
+# accel: goldens/p6_anim_fall.png
+env SIMCTL_CHILD_M3TE_FX=3 SIMCTL_CHILD_M3TE_ANIM_TIME=0.41 \
+    xcrun simctl launch --terminate-running-process booted co.swipelab.m3te
+# Settled board past the timeline — FX fully pruned, the move's final board. The
+# SAME settled frame backs all three of:
+#   goldens/p6_anim_after.png == goldens/p5_swap_after.png == goldens/p6_fx_after.png
+env SIMCTL_CHILD_M3TE_FX=3 SIMCTL_CHILD_M3TE_ANIM_TIME=2.0 \
+    xcrun simctl launch --terminate-running-process booted co.swipelab.m3te
+```
+
+`p6_anim_clear` / `p6_fx` / `p6_inputlock_board` are one and the same frame — the
+timeline's clear segment, the burst/popup FX, and the input-locked in-flight board
+are all the same committed-move moment — as are the three settled `*_after` goldens.
+
+The resting-board goldens — `goldens/p4_board.png`, `goldens/p4_hud.png`,
+`goldens/p9_polish.png`, and `goldens/p5_swap_before.png` (the swap's start pose) —
+are the seed-1337 board at rest, captured with no move committed:
+
+```bash
+# Resting candy board / HUD (no move): p4_board.png, p4_hud.png, p9_polish.png,
+# p5_swap_before.png
+SIMCTL_CHILD_M3TE_ANIM_TIME=0 \
+    xcrun simctl launch --terminate-running-process booted co.swipelab.m3te
+```
+
+They match `goldens/p6_idle_t0.png` over the board+HUD region (the `t==0` rest
+invariant, `tests/gem_pose.sx`); only the status-bar clock and the bottom
+home-indicator chrome vary per grab, never the board or HUD.
+
 ## Audio bank (P10) — final model
 
 The SFX bank (`audio.sx`) is a purely additive layer over iOS **System Sound