refactor(aidd-context): lean the project-memory skill for small models #1141

Problem

aidd-context:02-project-memory is 30 files and 7132 words: four actions (scan, write, check, sync), seven references (3503 words with the actions and router) and sixteen templates (3629 words). Every file a small model reads re-sends the whole context. The bank it writes is loaded in every session, so a wrong or stale fact costs more than its length.

Scope

• Same method as the assert and review skills: router with action paths, lean actions, references as tables, no rule stated twice.
• Stale facts (feat(aidd-context): a stale memory fact has neither a marker nor a trigger #942): a volatile fact (a count, a total, a date, a "currently N" line) is marked by a rule, and check flags it.
• Measure before and after on real projects: setup on a repository with no bank, refresh on a bank with drift injected (a stale count, a renamed path, a removed command, an architecture claim the code contradicts), graded blind.

Acceptance criteria

• The pre-commit gates pass, with fewer words than today.
• On the same projects, Claude haiku and sonnet and Qwen 3.8 Flash write banks with as many correct facts as the original and no more wrong ones, at lower or equal cost.
• A refresh flags every injected drift and writes nothing the user did not approve.
• A volatile fact has a rule, and check reports one gone stale.

Prior art in this repo

• refactor(aidd-dev): lean the assert skill for small models #1077 and refactor(aidd-dev): lean the review skill for small models #1078, and their protocol: real history replayed, defects injected into real changes, blind grading.
• feat(aidd-context): a stale memory fact has neither a marker nor a trigger #942, docs(aidd-context): document the Project Memory model and lifecycle #801, chore(framework): reshape the memory bank to its own templates #732.

Out of scope

• fix(aidd-context): preserve project-memory files on write failure #1018 (the memory hook's write failure) and fix(aidd-context): the memory hook wired into ~/.gemini/settings.json never runs under Antigravity, and fails silently #890 (hook placement under Antigravity): hook code, not the skill.
• feat(aidd-context): project memory points to the UI system instead of duplicating it #1123 (memory points to the UI system): depends on aidd-ui, whose PR feat(aidd-ui): govern UI systems and experience contracts #708 was closed.
• spike(aidd-context): prove portable access to host-native memory #882 (portable access to host-native memory).