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.

experiments/2026-05-12-cross-model-authoring/README.md

@@ -4,7 +4,7 @@ Empirical measurement of whether `.ail.json` or `.ail` is the form a
 foreign LLM author reaches for and succeeds with. Single subject for
 v1: Qwen3-Coder-Next via IONOS. Two blind cohorts; same four tasks.
 
-Parent spec: `docs/specs/2026-05-12-cross-model-authoring-form-test.md`.
+Parent spec: `docs/specs/0017-cross-model-authoring-form-test.md`.
 
 ## Layout
 

experiments/2026-05-12-cross-model-authoring/render/Cargo.toml

@@ -1,7 +1,7 @@
 # Empty `[workspace]` table declares this crate as a standalone
 # Cargo workspace of its own, so it is NOT auto-discovered as a member
 # of the root workspace at /home/brummel/dev/ailang/Cargo.toml. The
-# spec (`docs/specs/2026-05-12-cross-model-authoring-form-test.md`
+# spec (`docs/specs/0017-cross-model-authoring-form-test.md`
 # §Architecture lines 90-95) requires this experiment to live outside
 # the root workspace; the root Cargo.toml is intentionally not modified.
 [workspace]