Document public docs publication policy

[tamirat-wubie]

Boundary

Repository: mullusi/mullusi-docs
Surface: public documentation source
Change type: publication boundary policy

Causal Change

What changed:

• Added PUBLICATION_POLICY.md.
• Linked the policy from README.md documentation boundaries.

Why this change is required:

• The repository is public but had no explicit public-use boundary.
• Public docs need claim discipline for implemented, draft, roadmap, and research content.
• Mfidel documentation needs an explicit block against fidel-decomposition models.

What must not change:

• No broad legal license grant is introduced.
• No private roadmap, secret, or provider detail is exposed.

Verification

command: node --check assets/search.js; node scripts/validate-docs.mjs
result: PASS, docs validation passed

command: git diff --check
result: PASS

Governance

• No secrets, private keys, cookies, or provider tokens are committed
• Public/private boundary is clarified
• Rollback path is revert of commit 5ca05f0
• Mfidel atomicity boundary is preserved