docs: describe the finished roadmap and add community files

[Wahbeh-Mohammad]

What and why

All eleven roadmap phases (0–10) are merged, and every gem is still at 0.0.0 and unpublished. The root README, CLAUDE.md's opening and the community files still read as if the project were mid-build. Every claim below was re-derived from the tree (file counts, gate list, checklists, gemspecs), not copied from existing prose.

• README.md: a short pre-release status instead of the ~60-line phase-by-phase inventory. It has one row per gem (what the gem carries, its runtime dependencies), the supported Rubies (3.2–4.0, with async_http needing 3.3+) and the twenty-four gates, and it points at docs/first-release.md.
• CLAUDE.md: the ~240-line opening inventory is now a table with one row per gem and per layer, pointing at the as-built page and the checklists. The next step is named as the release path in docs/first-release.md. The stale (planned) markers are gone, and so is the "every checklist but … is still to be written" sentence. The phase workflow now says how post-v1 work follows it. The "Constraints that will bite", the command block and the probe-read claim sentences are unchanged in substance, and nothing about the frozen-chapter amendments or docs/deviations.md was touched. Net −250 lines.
• docs/README.md: knowledge/harvested/ and knowledge/notes/ exist, so their (planned) markers are dropped and the entries are linked.
• gems/dexpace-core/README.md: it now names the 8b and 8c adapter gems and drops "the adapter phase 8 ships". The other five gem READMEs were already accurate.
• CONTRIBUTING.md: it was written before gems/ existed. It now covers the real setup, the 24 gates, the Ruby range, the spec-driven contribution flow and the PR expectations.
• SECURITY.md: the "once it exists" wording is gone, and the in-scope list is concrete. The reporting channel is unchanged.
• .github/: bug-report and feature/requirement issue forms (they use the repository's type:bug / type:feature labels), config.yml (blank issues off, plus links to SECURITY.md and first-release.md), pull_request_template.md (requirement IDs, gates run, ledger and first-release records) and CODEOWNERS (@Wahbeh-Mohammad). The sibling nodejs-sdk has none of these to mirror. By the repository's convention, Markdown and YAML files carry no SPDX header.

Requirements

None. This is documentation only.

Verification

• bundle exec rake, all twenty-four gates, green on Ruby 4.0.6 (the .ruby-version development Ruby)
• ruby .claude/skills/housekeeping/probe.rb exits 0 before and after (nine checks)
• The issue forms parse as YAML

Note: on Ruby 3.4.10, test:gates' RequireAllowlistTest "rejects tsort … bundled at 4.1" fails locally, because 3.4's Gem::BUNDLED_GEMS::SINCE has no tsort entry. CI runs that gate on 4.0 only, so this is not a regression and has nothing to do with this change.