docs(lints): cross-reference allocation_policy.md from Cargo.toml + clippy.toml (Phase 6 follow-up, refs #193)

[githubrobbi]

Phase 6 §11.9 follow-up: parity with the Phase-5e panic_policy.md cross-reference precedent (PR #278).

The gap this closes

Cargo.toml and clippy.toml already point at panic_policy.md so a contributor running grep panic_policy Cargo.toml immediately finds the contract for the deny-level unwrap_used / expect_used / panic lints.

The same shape was missing for the allocation contract — a grep for allocation_policy Cargo.toml returned nothing before this change, defeating the discoverability that docs/architecture/code-quality/allocation_policy.md (PR #285) was designed to provide.

What this changes

Doc-comment-only edits. The [workspace.lints] block remains byte-identical at the TOML-value level — only trailing comments and the doc-block above # ───── Memory & allocation ───── gained content.

Cargo.toml (4 edits, 11 lines net)

1. New 5-line doc block above # ───── Memory & allocation ───── (line 460) mirroring the panic-policy block at line 322-326. Points at allocation_policy.md, the five-category taxonomy (α/β/γ/δ/ε), and the scripts/dev/clone_alloc_audit.sh script.

2. Per-lint trailing comments added to the relevant deny-level clone-family lints with section refs back into allocation_policy.md:

Lint	Section ref
clone_on_ref_ptr	§3.1 (category α — Arc clone)
redundant_clone	§3.4 (category δ — anti-pattern)
inefficient_to_string	§2 (lint posture)
str_to_string	§2
implicit_clone	§2
cloned_instead_of_copied	§2
map_clone	§2
assigning_clones	§2
rc_buffer	§3.1 (α)
rc_mutex	§3.1 (α)

clippy.toml (1 edit)

Extended the existing "Test code relaxations" comment block (which already references panic_policy.md) with a parallel paragraph referencing allocation_policy.md for the eight clone- and allocation-family lints. Lists each family lint explicitly so future contributors can grep on either lint name and find the contract.

Verification

• just lint-pre-push ✅ (86s) — every gate green: fmt-check, file-size, gates-drift, hooks-drift, workflow-drift, fast-drift, manifest-drift, commit-subjects, vet, vet-audit-discipline, machete, typos, reuse, cargo-check, lint-ci, lint-prod, lint-tests, rustdoc, doc-tests, tests, smoke, deny, lint-ci-windows.
• cargo metadata parses cleanly — TOML structure unchanged at value level.
• cargo clippy --workspace --all-targets emits zero diagnostics (lint values unchanged).
• Test count unchanged: 1,833 / 1,833 passing.

Behavior & contracts

• Zero functional change. The [workspace.lints] deny-set is byte-identical at the TOML value level.
• Public API unchanged.
• Doc-comments-only change.

Strict-lint posture

No suppression hacks. No new #[allow] / #[expect]. All edits are TOML doc comments.

Phase 6 closeout reference

Closes the only remaining Phase-6 follow-up item recorded in phase_6_final_report.md §11.9 #1 (local-only, gitignored under /docs/dev/). Plan §11.5 status moves from "Pending parity follow-up" to "Complete" after this PR lands.

refs #193