chore(release): v1.0.0 — the first stable release (M7.7)

[danielPoloWork]

Summary

Closes ROADMAP item 7.7 and Milestone 7 — the release PR that cuts v1.0.0, the first stable release. Bumps the version, seals the CHANGELOG, drafts the release notes, and refreshes the README. The public C ABI and C++ surface are frozen here under the SemVer 1.0 promise.

Motivation

Milestones 0–6 built and verified the pool; Milestone 7 polished it (docs site, README, packaging, audits) and accepted it against the spec (M7.6 / ADR-0029). M7.7 is the release ritual per ADR-0004 §2.

Changes

• version.hpp → MAJOR=1 MINOR=0 PATCH=0, VERSION_STRING "1.0.0"; the pool_smoke version-check TEST_CASE asserts the new components.
• CHANGELOG.md — [Unreleased] rolled into a sealed ## [1.0.0] — 2026-06-14 block (the M7.3 v1.0.0 headline, finalized, + the M7.1–M7.6 subsections); a fresh empty [Unreleased] restored; bottom link references rewritten ([Unreleased] → compare/v1.0.0...HEAD, new [1.0.0] → releases/tag/v1.0.0).
• docs/releases/v1.0.0.md — the human-prose release notes release.yml consumes as the GitHub Release body.
• README.md — status badge (green v0.6.0 observability → bright-green v1.0.0 stable), status paragraph, and milestone table (M7 → ✅ complete, M8 → ⏳ next).
• ROADMAP.md — 7.7 flipped + a v1.0.0 session checkpoint.

Design Patterns

• None — release mechanics. (All eleven adopted patterns were audited in M7.5.)

Verification

• Builds cleanly on the full toolchain matrix — the only source change is the version constants + the matching test assertion.
• Unit tests pass — built and ran pool_smoke locally (MSVC 19.51 + Ninja); the 1.0.0 version-check TEST_CASE passes, and CMake configured project(... VERSION 1.0.0) from version.hpp.
• clang-tidy / ASan / UBSan / Valgrind — unaffected; no behavioural change.
• markdownlint clean on the changed docs; the [1.0.0] / ROADMAP anchors follow the working v0.6.0 precedent.

Documentation Impact

• README.md updated — badge / status / milestone table.
• ROADMAP.md checkbox flipped — 7.7 + session checkpoint.
• ADR added/updated — N/A (release mechanics).
• docs/patterns/README.md updated — N/A.
• Spec updated — N/A.
• CHANGELOG.md updated — sealed [1.0.0] block.

After merge (the release ritual)

1. The maintainer reviews and merges this PR.
2. The agent tags v1.0.0 from master (ADR-0008); release.yml re-runs the matrix, builds the per-platform find_package-ready tarballs + SHA256SUMS, and drafts the GitHub Release from docs/releases/v1.0.0.md.
3. The maintainer clicks Publish on the draft GitHub Release (ADR-0004 §6).