docs: Mission makes Chromeria a personal app kept rebasable through modules

[lukemaj]

What: The Mission now describes Chromeria as the user's personal app, kept rebasable by putting fork features in their own modules instead of keeping upstream edits as small as possible.
Why: The user asked to drop the "smallest possible edits" constraint and personalize the app, while keeping every port modular so upstream rebases stay easy (#166 thread, 2026-10-08).
So what: Merging this updates Project Direction; later ports follow "modules first" instead of minimizing features.

Changes:

• MISSION.md: first paragraph rewritten; the Prism/OpenBot paragraph is unchanged. Triad total 1,389 characters (cap 1,500).
• docs/fork.md: "New files first" becomes "Modules first" (upstream-owned files carry only the hooks the modules need; ownership map and allowlist unchanged); intro says "personal, rebasable layer".

To revert: revert this commit.

Elon record

• Requirements and who asked: User: "we need to edit the mission and remove it. i want this app personalized", and "make sure that our port is as much modular as possible ... so upstream rebase is easy".
• Deleted: The "smallest possible edits" and "patch set shrinks" goals.
• Bottleneck: None; direction text only.
• Checked myself: Reread VISION, MISSION and OBJECTIVE together: the Mission still advances the Vision (one workspace on the open T3 core), and the Objective is unaffected.

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.5 KiB	13.5 KiB	+17 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	−8 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.4 KiB	6.5 KiB	+25 B (+0.4%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	56.2 KiB	56.3 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	13.5 KiB	13.5 KiB	−20 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	−3 B (−0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.5 KiB	6.4 KiB	−17 B (−0.3%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.0 KiB	57.0 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	9	9	0 (0.0%)	21	✅

Baseline: c1526a7 · PR result: 9a67250 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 114.0 KiB
• Claude decoded thread snapshot: 114.7 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.