docs: adopt dependencies-over-hand-rolling policy from NIH audit

A repo-wide Not Invented Here audit (ten parallel domain surveys covering
every package group, scripts/, native/, vendor/ edges, python/, test
infrastructure, and CI) asked of each hand-rolled surface whether a
maintained external package or Node builtin deletes it with a net win.

Policy: new implemented process note records that a dependency which
genuinely deletes owned code is a preferred simplification (bar: net
deletion, health, boundary fit, settled seams stay); root AGENTS.md
carries the one-line rule and dsh-find-simplifications now surveys for
hand-rolled-where-a-dependency-exists candidates.

Findings, all bilingual from birth:
- proposed/simplification: eventsource-parser for llm-deepseek SSE,
  node:timers/promises for three hand-rolled sleeps, turndown (or
  minimal 'entities') for tool-web HTML->markdown, gate-script
  consolidation onto mdast/parseArgs/globSync
- proposed/testing: execa + parseArgs + loadEnvFile + vi.waitFor for
  hand-rolled test subprocess plumbing
- proposed/process: pnpm/action-setup for symmetric CI caching
- proposed/feature: evaluate landstrip before building a Windows
  sandbox launcher
- rejected/simplification: ~30 swap verdicts recorded (vscode-jsonrpc,
  p-retry, Ajv, write-file-atomic, msw, hono, better-sqlite3, wireit,
  landstrip-for-linux, YAML consolidation, ...) so the survey is not
  re-litigated from scratch

Also drops the stale prompt/ entry from the AGENTS.md layout map
(workspace instructions live in packages/context/workspace-context).

scripts/doc-budgets.manifest.json

@@ -1,5 +1,5 @@
 {
-  "AGENTS.md": 1680,
+  "AGENTS.md": 1700,
   "docs/AGENTS.md": 1150,
   "docs/architecture.md": 1800,
   "docs/cordis-primer.md": 600,