docs(agents): qualify line 8's DB-column item — control plane vs. the metadata tables (#13431)

`AGENTS.md:8` presents `environment_id` as one of five flagship surfaces of the
v5.0 `project` -> `environment` rename, closing with "No aliases." Measured on
`origin/main`, that item is under-qualified in BOTH directions, and the two
errors point opposite ways:

  * On the METADATA tables the column is retired. `sys_metadata` still declares
    it, but only as a deprecated nullable legacy column that no writer writes
    and the uniqueness discriminator excludes; `sys_metadata_history` dropped it
    from its declaration outright in the ADR-0008 SS0 branch/project-removal
    amendment. A reader taking line 8 at face value learns to write
    `environment_id` into new metadata rows; the spec's own describe() strings
    say new code must use `organization_id` only.

  * On the CONTROL PLANE the column is fully live and enforced.
    `sys_environment_member` is keyed `(environment_id, user_id)` and the
    runtime HTTP dispatcher filters on it for the per-project membership 403
    gate. So a flat "since deprecated" qualification -- or dropping the item --
    would teach the opposite error.

The edit therefore carries the SCOPE rather than a single verdict, in place and
line-neutral. The v5.0 rename statement is untouched: the rename happened, and
the deprecation sits on a later and different axis (environment -> organization,
not project -> environment).

Line-neutral by construction and measured: AGENTS.md stays at 1162 lines
(ceiling 1162, headroom 0) and the widest table row stays 1081 bytes at L720
(pin 1081, headroom 0) -- line 8 is a blockquote, not a table row, so neither
byte ratchet meters it, and the gate's own `scanLineLengths` reports 0 offenders
with line 8 classified `blockquote`.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: claude[bot]

AGENTS.md

@@ -5,7 +5,7 @@ Read natively by Claude Code, GitHub Copilot (coding agent + CLI), and other age
 separate `.github/copilot-instructions.md` mirror needed. When any other instruction file
 in this repo (including `.claude/skills/**`) conflicts with this one, **AGENTS.md wins**.
 
-> **v5.0 breaking rename: `project` → `environment`** everywhere (CLI `-e`, `/api/v1/environments/:id`, header `X-Environment-Id`, `OS_ENVIRONMENT_ID`, DB column `environment_id`). No aliases. See ADR-0006. "Project" now only means the npm/monorepo sense.
+> **v5.0 breaking rename: `project` → `environment`** everywhere (CLI `-e`, `/api/v1/environments/:id`, header `X-Environment-Id`, `OS_ENVIRONMENT_ID`, DB column `environment_id` [control-plane tables; on the metadata tables since deprecated in favour of `organization_id`, ADR-0006 v4]). No aliases. See ADR-0006. "Project" now only means the npm/monorepo sense.
 
 This file carries principles, binding rules and lookup tables. Lessons from past
 incidents are distilled in place — failure mode, discipline, boundary — without