Remove the last compiler dependency on sema as semantic truth and stop
publishing as-you-type sema diagnostics from the LSP.
- core.zig: drop dead `Compilation.analyze()`, the `sema_result` field,
and the sema->diagnostics merge; drop the now-orphaned sema import.
The CLI pipeline (parse -> resolveImports -> generateCode) never called
analyze(), so this removes only dead code.
- lsp/server.zig: rename `analyzeAndPublish` -> `refreshEditorIndex` and
delete its sema-diagnostic publish (and the now-unused `semaToLspDiags`).
The editor index (doc.sema) is still refreshed for nav/refs/completion/
tokens. On-save/on-open diagnostics still come solely from the canonical
compiler pipeline in `runProjectCheck` (unchanged).
- Document sema as an editor-indexing API (doc.sema field comment).
Intended behavior change: as-you-type sema diagnostics no longer publish;
on-save canonical diagnostics are the sole source. CLI compile output and
the 361-example suite are unchanged (361/0, zero snapshot churn).
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