docs: fix three stale cross-references left behind by earlier renames #1106

Summary

Three independent, one-line documentation staleness bugs, small enough to fix in one PR and each verifiable on its own: the PR template links a deleted AGENTS.md, two docs still stamp themselves as the v0.0.27 tree (current version is 0.5.0-beta.1), and docs/README.md omits code-guidelines.md from its index.

Background

7a. .github/PULL_REQUEST_TEMPLATE.md:3 reads "For the full contributor contract see AGENTS.md and CONTRIBUTING.md." AGENTS.md does not exist at the repo root, and CONTRIBUTING.md no longer references it. CHANGELOG.md:82 records that PR #1014 replaced the dead AGENTS.md links in CONTRIBUTING.md; it fixed CONTRIBUTING.md and missed the PR template, the surface every contributor sees on their first pull request.

7b. Cargo.toml is at 0.5.0-beta.1, but two docs still name a much older tree: docs/supported-models.md:3 ("summarizes model-family support in the v0.0.27 source tree") and docs/turbo-kv-cache.md:167 ("As of v0.0.27, the hard-coded allowlisted model-type prefixes are:"). This is a stamp problem, not a content problem: the three prefixes turbo-kv-cache.md:169-171 lists (qwen3_5, qwen3_5_moe, qwen3_next) still match src/lib/mlxcel-core/src/cache/turbo/allowlist.rs:102-104 exactly. supported-models.md is the page CONTRIBUTING.md and README.md both point readers to for the maintained support matrix, so the stale stamp reads as "many releases out of date" even where it is current.

7c. docs/README.md enumerates 18 GitHub-facing documents. docs/ contains 19 (excluding README.md). The one missing entry is code-guidelines.md, which CONTRIBUTING.md names as one of the three core contract documents alongside architecture.md and adding-models.md, both of which are indexed.

Proposed Solution

• 7a: point the PR template at CONTRIBUTING.md and docs/code-guidelines.md, where the contract lives now.
• 7b: drop the v0.0.27 version stamp in favour of the "source of truth is the code" pointers supported-models.md:4-8 already carries. A stamp that nothing checks will go stale again; dropping it is more durable than bumping it.
• 7c: add code-guidelines.md to the numbered list with a one-line description covering the // Used by: shared-function convention and the JIT kernel dtype cache-key rule.

Implementation Notes

• No code or behavior change; docs only.
• Related: 7c overlaps docs(core): the three shared functions code-guidelines.md names as its own example carry no // Used by: annotation #1110, which addresses the missing // Used by: annotations that code-guidelines.md itself calls out.

Acceptance Criteria

• No reference to AGENTS.md remains outside CHANGELOG.md (historical entries stay).
• No v0.0.27 reference remains in docs/.
• ls docs/*.md and the docs/README.md list agree.
• Docs only; no code or behavior change.

Original Suggestion

Title: docs: three stale cross-references left behind by earlier renames

Three independent, individually one-line documentation staleness bugs. Small enough to
fix in one PR; each is verifiable on its own.

7a. .github/PULL_REQUEST_TEMPLATE.md still points at a deleted AGENTS.md

.github/PULL_REQUEST_TEMPLATE.md:3:

For the full contributor contract see AGENTS.md and CONTRIBUTING.md.

AGENTS.md does not exist at the repository root. CHANGELOG.md:82 records that this was
supposed to have been handled:

The dead AGENTS.md links in CONTRIBUTING.md are replaced (PR #1014).

That PR fixed CONTRIBUTING.md and missed the PR template, which is the surface every
contributor sees on their first pull request.

Fix: point at CONTRIBUTING.md and docs/code-guidelines.md, which is where the
contract actually lives now (CONTRIBUTING.md links both).

7b. Two docs claim to describe the v0.0.27 source tree

Cargo.toml is at 0.5.0-beta.1. Two documents still name a much older tree:

• docs/supported-models.md:3 — "This page summarizes model-family support in the v0.0.27 source tree."
• docs/turbo-kv-cache.md:167 — "As of v0.0.27, the hard-coded allowlisted model-type prefixes are:"

supported-models.md is the page CONTRIBUTING.md and README.md both send readers to
for the maintained support matrix, so the version stamp reads as "this list is many
releases out of date" even where it is current.

Note this is a stamp problem only, not a content problem: the three allowlisted prefixes
turbo-kv-cache.md:169-171 lists (qwen3_5, qwen3_5_moe, qwen3_next) still match
src/lib/mlxcel-core/src/cache/turbo/allowlist.rs:102-104 exactly. Nothing behind either
stamp needs rewriting.

Fix: either update both to the current version, or drop the version stamp in favour of
the "source of truth is the code" pointers supported-models.md:4-8 already carries. The
second is the more durable choice — a stamp that nothing checks will go stale again.

7c. docs/README.md index omits code-guidelines.md

docs/README.md enumerates 18 GitHub-facing documents. docs/ contains 19 (excluding
README.md itself). The missing entry is code-guidelines.md — which CONTRIBUTING.md
names as one of the three core contract documents, alongside architecture.md and
adding-models.md, both of which are indexed.

Fix: add it to the numbered list with a one-line description covering the // Used by:
shared-function convention and the JIT kernel dtype cache-key rule.

Acceptance criteria

• No reference to AGENTS.md remains outside CHANGELOG.md (historical entries stay).
• No v0.0.27 reference remains in docs/.
• ls docs/*.md and the docs/README.md list agree.
• Docs only; no code or behavior change.