Enhance documentation for format-datetime library and contributor guidelines

[pphatdev]

Summary

• Bump package to 0.3.5 across package.json, deno.json, and jsr.json (three-file bump as required by the dual-publish model).
• Rename repository references from format-datetime → khmer-datetime in package.json (repository.url, homepage, bugs.url). The npm/JSR package name is unchanged (@pphatdev/format-datetime).
• Add a full docs/ set (10 files) covering getting started, tokens, API reference, TypeScript, lunar calendar, algorithms, architecture, runtimes, examples, and FAQ.
• Add llms.txt at the repo root following the llmstxt.org spec, pointing LLM tools at every doc and source file via raw.githubusercontent.com/pphatdev/khmer-datetime/... URLs.
• Add an AI Agent Guidelines section to README.md linking to CLAUDE.md and llms.txt, plus a list of load-bearing invariants (longest-token-first regex, .ts import extensions, no Node built-ins in src/, UTC-noon normalization in the lunar solver, three-file version bumps, dual-runtime test parity, globalThis attachment, defualtPatterns typo, KhmerDate placeholder methods).
• Add a GitHub Actions workflow to publish to npm and GitHub Packages on release (.github/workflows/npm-publish.yml).
• Bump postcss 8.5.18 → 8.5.26 (Dependabot, transitive dev-only).

Commits (non-merge)

• a30bc09 docs: add documentation structure and AI agent guidelines for contributors
• 4528b2f docs: add comprehensive documentation for format-datetime library tokens and usage
• 3777b80 chore: update repository URL, homepage, and bug tracker links to reflect project rename
• 5d7841b / 1cba8ce feat: add GitHub Actions workflow to automate NPM and GitHub package publishing
• badb530 chore: bump version to 0.3.5
• 18cb4d5 build(deps): bump postcss from 8.5.18 to 8.5.26

Files changed

 .github/workflows/npm-publish.yml |   1 +
 README.md                         |  55 ++++
 deno.json                         |   2 +-
 docs/algorithms.md                | 388 +++++
 docs/api-reference.md             | 569 +++++
 docs/architecture.md              | 318 +++
 docs/examples.md                  | 494 +++++
 docs/faq.md                       | 244 +++
 docs/getting-started.md           | 201 +++
 docs/lunar-calendar.md            | 339 +++
 docs/runtimes.md                  | 266 +++
 docs/tokens.md                    | 289 +++
 docs/typescript.md                | 303 +++
 jsr.json                          |   2 +-
 llms.txt                          |  49 +++
 package-lock.json                 |  18 +-
 package.json                      |  10 +-
 17 files changed, 3532 insertions(+), 16 deletions(-)

No src/ or test/ files change in this PR — this is a docs, infra, and version-bump release only.

Verification

• npm run build succeeds (dist artifacts produced for cjs, esm, iife + .d.ts).
• npm run test passes on Node (Vitest) and Deno (@std/testing + @std/expect).
• package.json, deno.json, jsr.json all show 0.3.5.
• package.json repository.url, homepage, and bugs.url all point to khmer-datetime.
• llms.txt links resolve (spot-check a few raw.githubusercontent.com/pphatdev/khmer-datetime/... URLs).
• After merge and release tag, the new npm-publish.yml workflow completes green.

Risk

Low. No runtime source changes, no API surface changes, no test changes. The repository URL rename is metadata-only — the published package name stays @pphatdev/format-datetime on both npm and JSR.