docs: sync main README with develop

.agent/context/20261008T165709Z-sync-main-readme.md

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+# Session Context: sync main README
+
+## Date/time
+
+- UTC: 2026-10-08T16:57:09Z
+
+## User goal
+
+Make main README match develop via a new documentation-only PR.
+
+## Original prompt/request
+
+User asked to make README the same as develop, then accepted updating main.
+Prior instruction: never reopen closed PRs; skip FreePi for this work.
+
+## Assumptions
+
+- Sync README and its linked developer guide; other develop changes excluded.
+- Main is explicitly selected target; branch from main for scoped comparison.
+
+## Plan
+
+1. Copy exact documents from develop, check links and Markdown, create draft PR.
+
+## Key decisions
+
+- Source develop: 55a387abad228d61c7a0a7a911299c103495bda0.
+- No application or deployment configuration changes.
+- No merge by agent.
+
+## Files/components touched
+
+- README.md and docs/DEVELOPER_GUIDE.md: exact develop versions.
+- This session context.
+
+## Commands/checks
+
+- Exact source equality and relative links: checked before commit.
+- Pinned repository-wide Markdown lint: run before commit.
+- git diff --check: run before commit.
+
+## External-doc findings
+
+- None; copy existing documentation without new integration claims.
+
+## Unresolved questions
+
+- None.
+
+## Git and PR state
+
+- Branch: docs/sync-main-readme.
+- Base main: 319b0758147622e8f25930e6663884a252f86dd1.
+- Commit/PR: created after validation; new draft targets main.
+- CI: pending at creation.
+
+## Review gates
+
+- Gate A and B: SKIPPED per explicit user instruction to omit FreePi.
+- No passing review claimed; remains draft.
+
+## Handoff/next steps
+
+1. Human review and merge; closed PRs remain untouched.