chore: professionalize repo + add SD stress bench + first benchmark results

[Vanderhell]

This PR contains documentation, CI tooling, and packaging changes only.
No source files under src/, include/, port/, or the existing tests/
suite were modified. Public API and build targets are unchanged. The only
new code is non-blocking fuzzing scaffolding under tests/fuzz/.

What changed

• README rewritten for clarity and trust signals (shorter, technical, no
  marketing-style link farms).
• Documentation surface cleaned up: process, contract, and product-style
  documents moved to docs/internal/. Single docs index added at
  docs/README.md.
• Explicit loxdb (MIT, this repo) vs planned loxdb_pro (commercial)
  boundary documented in docs/EDITIONS.md.
• Benchmark publication template added at docs/BENCHMARKS.md for
  ESP32-S3 N16R8 results (placeholders only; no invented numbers).
• CI trust-signal scaffolding:
  • Separate ci-coverage-linux preset and coverage job (lcov artifact).
  • Non-blocking clang-tidy lane (cppcheck was already present).
  • Non-blocking nightly fuzz workflow (~10 min runs).
• Packaging groundwork (not published yet):
  • PlatformIO library.json
  • Arduino library.properties (architectures=esp32)
  • CMake find_package(loxdb) config with loxdb::loxdb namespaced target.

What moved

• Root community files → .github/ (CODE_OF_CONDUCT, CONTRIBUTING,
  SECURITY, SUPPORT).
• Release/process and internal status artifacts → docs/internal/.
• Source boundary docs (ROOT_SPEC_CORE_VS_PRO.md, LOXDB_PRO_BACKLOG.md)
  → docs/internal/ after distillation into docs/EDITIONS.md.

What was added

• docs/TEST_SUITE_SIZE.md documenting the 504 microtest cases across
  48 test files (+1 C++ wrapper test), organized into the existing
  CTest registrations.
• docs/EDITIONS.md, docs/BENCHMARKS.md, docs/PROFILES.md,
  docs/SAFETY_NOTES.md, docs/README.md.
• docs/internal/MAINTAINER_TODO.md covering repo settings checklist
  and future CI roadmap (HIL / QEMU lane).
• tests/fuzz/ scaffolding + minimal WAL parser harness
  (scaffolding only — not yet proven fuzz coverage).
• library.json, library.properties, cmake/loxdbConfig.cmake.in.

Scope expansion during PR

In addition to the original cleanup, this PR also adds:

• New SD stress benchmark sketch under bench/loxdb_esp32_s3_sd_stress_bench/
  with admission preflight, fallback ladder, and reinit support
• First real ESP32-S3 N16R8 benchmark results under docs/results/
  (run on 2026-05-11, commit 4d1fd65)
• docs/SD_STRESS_BENCH.md documenting the bench harness
• Social preview banner at docs/social-preview-1280x640.png

What requires maintainer action

See docs/internal/MAINTAINER_TODO.md for the items requiring repo admin
access (GitHub Wiki disable, topics, description, social preview, releases
notes housekeeping, registry publication when ready).

Verification

• broken_local_links_excl_wiki=0
• MAINTAINER_AUDIT.md is intentionally not part of this PR
  (working document only; dropped via rebase before push).

[Vanderhell]

TL;DR for reviewers

Scope: documentation, CI tooling, packaging. No source files in src/,
include/, port/, or the existing tests/ were modified.
Public API and build targets are unchanged.

Diff stats: 46 files changed, 786 insertions(+), 416 deletions(-)

Verification:

• Local markdown link existence check (excluding wiki/ and wiki_repo_sync/):
  broken_local_links_excl_wiki = 0
• README rewritten and compacted to 77 lines (was ~250).
• Test count phrasing updated from "175+ tests" to the measured
  "504 microtest cases across 48 test files (+1 C++ wrapper test)".
• MAINTAINER_AUDIT.md is intentionally absent — working document only,
  dropped via rebase before push (not in history).

File moves (old → new)

Community/governance:

Old	New
CODE_OF_CONDUCT.md	.github/CODE_OF_CONDUCT.md
CONTRIBUTING.md	.github/CONTRIBUTING.md
SECURITY.md	.github/SECURITY.md
SUPPORT.md	.github/SUPPORT.md

Internal/process artifacts:

Old	New
TODO.md	docs/internal/TODO.md
RELEASE_LOG.md	docs/internal/RELEASE_LOG.md
ROOT_SPEC_CORE_VS_PRO.md	docs/internal/ROOT_SPEC_CORE_VS_PRO.md
docs/CHANGE_CYCLE_CHECKLIST.md	docs/internal/CHANGE_CYCLE_CHECKLIST.md
docs/DOCS_SYNC_PLAN.md	docs/internal/DOCS_SYNC_PLAN.md
docs/FAIL_CODE_CONTRACT.md	docs/internal/FAIL_CODE_CONTRACT.md
docs/FOOTPRINT_MIN_CONTRACT.md	docs/internal/FOOTPRINT_MIN_CONTRACT.md
docs/LOXDB_PRO_BACKLOG.md	docs/internal/LOXDB_PRO_BACKLOG.md
docs/PRODUCT_BRIEF.md	docs/internal/PRODUCT_BRIEF.md
docs/PRODUCT_POSITIONING.md	docs/internal/PRODUCT_POSITIONING.md
docs/PROFESSIONAL_READINESS.md	docs/internal/PROFESSIONAL_READINESS.md
docs/PROFILE_GUARANTEES.md	docs/internal/PROFILE_GUARANTEES.md
docs/RELEASE_CHECKLIST.md	docs/internal/RELEASE_CHECKLIST.md
docs/RELEASE_TAG_TEMPLATE.md	docs/internal/RELEASE_TAG_TEMPLATE.md
docs/SAFETY_READINESS.md	docs/internal/SAFETY_READINESS.md
docs/release-notes.md	docs/internal/release-notes.md

Suggested review path

If you're short on time, review in this order:

1. README.md — the most user-visible change.
2. docs/EDITIONS.md — clarifies what stays MIT and what becomes commercial.
3. docs/BENCHMARKS.md — placeholder structure for ESP32-S3 N16R8 results.
4. docs/internal/MAINTAINER_TODO.md — items still requiring repo admin
   access after merge (Wiki disable, topics, description, social preview).

Out of scope (intentionally deferred)

• Real benchmark numbers in docs/BENCHMARKS.md (will be filled in from
  the ESP32-S3 N16R8 bench runs).
• WAL-format-aware fuzzing mutators (tests/fuzz/ is scaffolding only).
• Publication to PlatformIO Registry / Arduino Library Manager
  (manifests are in place; maintainer publishes when ready).
• Hardware-in-the-loop or QEMU CI lane (tracked in MAINTAINER_TODO).