refactor(ffi-linkage)!: Phase 9.0 — delete the hash_foreign token (src is foreign-free)

Per user directive (total purge): remove the hash_foreign token entirely rather than
keep it for a friendly deprecation message. Deleted: the token enum (token.zig), the
lexer keyword entry + directive-list mention + lex test (lexer.zig), the 4 parser
rejection sites + 2 lookahead clauses + the runtime-class prefix #foreign peek arm
(parser.zig), and the lsp completion arm (server.zig). '#foreign' now lexes as an
invalid '#' token → a generic 'expected ;' parse error (no migration hint — the
accepted UX cost of zero-foreign). Deleted examples/1176-diagnostics-foreign-removed
(its purpose, the friendly rejection, no longer exists).

src/ now contains ZERO 'foreign' (case-insensitive). Suite green (645 corpus / 443
unit, 0 failed). Remaining for the 9.4 gate: issues/*.md prose + example filenames.

src/token.zig

@@ -118,7 +118,6 @@ pub const Tag = enum {
     hash_insert, // #insert
     hash_builtin, // #builtin
     hash_compiler, // #compiler
-    hash_foreign, // #foreign
     hash_library, // #library
     hash_framework, // #framework
     hash_using, // #using