docs: add complete product guide and refresh technical book

[BenAlaa]

Outcome

T3 Code Decoded now starts with a complete product guide and then provides the source-grounded technical field guide. Readers can understand how to install, configure, use, supervise, review, update, and troubleshoot T3 Code before tracing the implementation boundaries behind those workflows.

Scope

• Added the product chapters covering onboarding, environments, projects, composer context, providers, workbench, source control, remote/background work, mobile, devices, personalization, usage, updates, recipes, and troubleshooting.
• Refreshed the technical route across eight parts, including Antigravity, device hosts, mobile behavior, remote access, T3 Connect, release/update ownership, telemetry, and recovery boundaries.
• Updated the cover, reading guide, contents, README, book plan, chapter numbering, figures, source references, and source lock.
• Read and integrated the local upstream docs/ tree at 859304b78 without duplicating facts across chapters.
• Removed the internal synthesis/transfer chapters and labs from the public edition and rewrote this branch so that transfer material is absent from its commit history.

Non-goals

• No product implementation code was changed.
• No upstream source files were modified.
• The private archive repository was not changed.

Evidence

• Canonical source lock: sources/t3code.lock.json, pinned to 859304b7808ab9a4be87b1bddcd07c6485bf9c4f.
• Primary anchors: src/content/book/00-cover.mdx, 01-how-to-read.mdx, 02-contents.mdx, product chapters, and technical chapters through Chapter 53.
• Claim classes remain labeled as verified behavior, documented intent, inference, or future/proposed where applicable.

Validation

• npm test — 49 tests passed
• npm run build — 59 pages built and validated
• Source validation — 181 excerpts and 525 pinned references verified
• Transfer/synthesis absence test passed
• Source links, headings, search index, accessibility fallbacks, and print states checked

Review focus

• Confirm the product-first reading order and chapter ownership boundaries.
• Review the source lock and provider/device/release coverage.
• Confirm that repeated facts remain linked to their primary chapter rather than duplicated.

Co-authored-by: Codex [email protected]