convention: counter-prefix file naming across docs/specs/, docs/plans/, design/contracts/, design/models/

All 176 files in the four accumulating directories now use a
zero-padded 4-digit counter prefix that reflects creation order
(`NNNN-slug.md`). The counter is assigned per directory in strict
git-log creation order; ties broken alphabetically by original name.
The old `YYYY-MM-DD-` prefix on docs/specs/ and docs/plans/ files is
dropped — the date is recoverable from git log and the counter
carries the ordering.

A file's counter is stable for the life of the file: never reassigned,
never reused, never compacted. Deleted files retire their counter;
subsequent files do not fill the gap. This is the property that lets
cross-references stay literal — refs use the full filename including
the counter (`design/contracts/0007-honesty-rule.md`) so they grep
cleanly and resolve directly without a glob step.

313 cross-references updated across .md/.rs/.toml/.c/.json files
(test pins, include_str! paths, design-INDEX entries, baseline notes,
runtime C comments, inter-contract markdown links incl. bare basename
and `../models/foo.md` forms).

CLAUDE.md gets a new "File-naming convention" section spelling out
the rule and rationale. skills/brainstorm/SKILL.md and
skills/planner/SKILL.md updated so new spec/plan creation produces
counter-prefixed names from the start.

The full test suite (cargo test --workspace) passes.

crates/ailang-codegen/tests/embed_record_layout_pin.rs

@@ -1,4 +1,4 @@
-//! FROZEN ABI byte-pin — see design/contracts/frozen-value-layout.md.
+//! FROZEN ABI byte-pin — see design/contracts/0006-frozen-value-layout.md.
 //! Pins the heap (@ailang_rc_alloc) box layout a boundary-crossing
 //! single-ctor scalar record takes: size = 8 + n*8, tag i64 @ offset
 //! 0, fields i64-strided from offset 8. Goes RED if codegen moves an

crates/ailang-codegen/tests/embed_staticlib_lowering.rs

@@ -45,7 +45,7 @@ fn staticlib_emits_forwarder_no_main() {
 
 /// M3: a single-ctor scalar record param/ret crosses the embedding
 /// C boundary as a bare `ptr` (the frozen payload pointer —
-/// design/contracts/frozen-value-layout.md). The M2 forwarder body
+/// design/contracts/0006-frozen-value-layout.md). The M2 forwarder body
 /// is byte-unchanged: leading `ptr %ctx`, TLS save/store/restore, the
 /// internal `@ail_<module>_<fn>` call carrying no ctx arg and no
 /// aggregate calling convention (no `sret`/`byval` — a record is a