Add CI workflow and README; close remaining MASTER_PLAN quality gates

[Copilot]

The project had working code and tests but no CI and no user-facing documentation — the two remaining unchecked items blocking v1 readiness per MASTER_PLAN.md.

CI (.github/workflows/ci.yml)

Two jobs:

• Lint & Required Tests — type-checks with tsc --noEmit and runs bun run test:required (unit + 5 core integration tests, no optional tools needed). This is the blocking gate.
• Optional Tests — installs unzip, poppler-utils, tesseract-ocr from apt, bootstraps PDF/EPUB fixtures, then runs the full suite. Isolates optional-tool regressions from core failures.

Both jobs use permissions: contents: read (minimal GITHUB_TOKEN scope).

README

Covers installation, all CLI commands and flags, the complete 13-format support matrix with support levels, optional dependency table, source manifest usage, sample frontmatter output, and development workflow.

MASTER_PLAN.md

Marked CI, README, and the already-completed Release Quality Gates as done. Remaining open items: live YouTube transcript regression and live CNN URL regression.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Review and offer next steps</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Review and offer next steps #3

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