docs: version single-source sweep + fix dead README links

[thinmintdev]

Summary

• Sweeps stale version strings in README.md, CONTRIBUTING.md, PLAN.md, and manifest.json to match pyproject.toml (0.3.2-alpha.1); pyproject is the single source of truth (closes docs: version single-source sweep (README/CONTRIBUTING/PLAN/manifest -> pyproject) #617)
• Fixes dead doc links in README.md, CHANGELOG.md, and installer/README.md: docs/api/mcp.md → docs/mcp/overview.md, docs/api/agents.md → docs/agents/overview.md, and docs/v0.2-upgrade.md → https://hal0.dev/docs/v0.2-upgrade hosted URL (closes docs: fix dead README doc links (mcp/agents -> overview.md; recreate-or-redirect v0.2-upgrade.md) #628)

Scope

Only doc/version files touched — no source, no tests, no graphify noise:

• CONTRIBUTING.md — version string (line 3)
• PLAN.md — version string + status date (line 10)
• README.md — version string + three dead links
• manifest.json — cosmetic version field
• CHANGELOG.md — dead v0.2-upgrade.md link → hosted URL
• installer/README.md — dead v0.2-upgrade.md links → hosted URL (2 occurrences)

Note on #642

PR #642 (DCO governance) also edits CONTRIBUTING.md but in a different section (adds DCO sign-off block). No line conflict — #642 will need a rebase after this merges, but no manual fixup required.

Test plan

• Verify README.md status badge shows v0.3.2-alpha.1
• Verify CONTRIBUTING.md line 3 shows v0.3.2-alpha.1
• Verify PLAN.md status line shows v0.3.2-alpha.1
• Verify manifest.json version field is 0.3.2-alpha.1
• Click README mcp/agents links — confirm they resolve to docs/mcp/overview.md and docs/agents/overview.md
• Click v0.2-upgrade links in README/CHANGELOG/installer README — confirm they go to https://hal0.dev/docs/v0.2-upgrade

🤖 Generated with Claude Code

[thinmintdev]

REVIEWER VERDICT: APPROVE (comment-form — self-approval blocked). CI green. Docs-only.

SPEC (#617 + #628): All ACs met.
#617 — every shipped version string reconciled to pyproject 0.3.2-alpha.1: README (×2: "at v0.2.0"→"v0.3.2-alpha.1" + status line), PLAN.md status, CONTRIBUTING.md, manifest.json (0.1.0-alpha.1→0.3.2-alpha.1). pyproject is the single source of truth.
#628 — dead links fixed: docs/api/mcp.md→docs/mcp/overview.md and docs/api/agents.md→docs/agents/overview.md (verified: old targets were absent on main; new targets exist in-repo — confirmed docs/mcp/overview.md + docs/agents/overview.md on the branch). All v0.2-upgrade.md refs (README ×3, CHANGELOG, installer/README) repointed to the hosted https://hal0.dev/docs/v0.2-upgrade — the approach #628 prefers and CONTEXT.md already uses.

STANDARDS: No scope creep, no leaks. Link targets verified to resolve.

Merge-ready. CONFLICT NOTE below (see report) — #643 touches CONTRIBUTING.md top (lines 1-6); overlaps #642 (DCO, lines 2-13).