docs(pre-0.0.22): env bound tightened, panel RFC-0006 citations

[Xuepoo]

Priority: P1 | Area: docs | Labels: docs,P1,area:docs | Milestone: v0.1.0 | RFC: OQ-058 | Task: CTX-0081

Docs-only sync to pre-0.0.22 release state. No implementation claims. English-only.

Changes:

• env: host Lua-call key-shape bound updated from stale 128/E_DEF_* to ^[A-Z_][A-Z0-9_]*$ 1..64 E_ENV_KEY_INVALID per bitty#1751 via #1752 (closes #381 divergence); pins moved to bitty@c2aaf218; default-host not_implemented status kept.
• file-manager/git-panel/roadmap: cite RFC-0006 predecessor (bitty-docs#443 OPEN/#445 merged); rows stay deferred with owning-repo follow-ups.
• Version stays 0.0.21; no 0.0.22 pre-claim.

Verified against bitty main c2aaf218. Do NOT merge.

[Xuepoo]

Independent review (read-only) — reviewer: ctx-0081-reviewer-20261007 — Verdict: APPROVE

Spot-checks vs bitty main c2aaf218 (PR head bd308ac):

1. env bound 64/E_ENV_KEY_INVALID — PASS. env.md retires 128/E_DEF_INVALID/E_DEF_LIMIT, now ^[A-Z_][A-Z0-9_]*$ 1..64 E_ENV_KEY_INVALID, pins to bitty@c2aaf218. Matches host.rs ENV_KEY_MAX_BYTES=64 + validate_env_key at c2aaf218; default-host not_implemented status kept.
2. RFC-0006 citations — PASS. file-manager/git-panel/roadmap cite accepted contract text in RFC-0006, bitty-docs#443 OPEN/#445 merged. Verified #443 OPEN, #445 MERGED 2026-10-07.
3. rows stay deferred — PASS. Presentation stays deferred / candidate non-normative, owning-repo follow-ups, no implementation claim. Version stays 0.0.21, no 0.0.22 pre-claim. English-only (non-ASCII = em-dashes in context only).
4. CI green — PASS. Docs quality pass x2 + Secret scan pass x2.

Do NOT merge per PR body — review only.