Prepare Vectorless RAG v0.2.0 research preview

[gcharang]

Change

Prepare the public repository for the source-only v0.2.0 research preview under the MIT License.

• add licensing, release metadata, community health files, and GitHub templates
• replace manual secret setup with an atomic non-overwriting initializer
• add documentation, link and anchor validation, and complete task-oriented navigation
• add an isolated PostgreSQL integration gate to local CI and GitHub Actions
• pin every GitHub Action to the planned immutable commit and Helm v4.2.3
• preserve research-preview limits, provider-cost controls, and the existing live release gate

Content plan and review focus

The release-readiness plan supplied for this work is the content plan. Review the environment initializer, isolated cleanup boundary, documentation contracts, release metadata consistency, and CI pins. No hosted preview applies because this change publishes source documentation and repository configuration.

Verification

• make install
• make docs-check
• make api-check: 363 passed, 6 infrastructure tests skipped in this tier
• TEST_POSTGRES_PORT=55433 make test-integration-stack: 6 passed
• make web-check: 31 tests passed and React Doctor 100/100
• make playwright-install: Chromium and operating-system dependencies verified by launch
• CHOKIDAR_USEPOLLING=1 make playwright: 20 passed, paid live test skipped
• make deploy-check ENV_FILE=.env.example with checksum-verified Helm v4.2.3
• make docker-build
• TEST_POSTGRES_PORT=55433 CHOKIDAR_USEPOLLING=1 make ci with Helm v4.2.3
• git diff --check

Port 55432 is occupied on the verification host, so the documented override used 55433. The host inotify quota is exhausted, so Playwright used polling. CI uses its clean default environment.

Security and provider cost

No provider credential was read or added to CI. All completed gates were provider-free. The paid one-PDF DeepSeek live gate remains blocked until this PR merges and push CI passes on the exact merge commit.

AI-use disclosure

OpenAI Codex based on GPT-5 implemented the supplied handoff plan, audited and rewrote documentation with the repository writing guidelines, added tests, and ran verification. Every diff and command result was reviewed before this PR.