docs: v1 release plan and engineering notes

[hadifarnoud]

Summary

Adds docs/v1-release-plan.md — a self-contained handoff/working doc for taking Hexa to a stable v1.0.0, written so a future session (or contributor) can pick up cold.

It captures:

• Orientation — what Hexa is, default branch is master, local verification commands.
• Current state — every merged bug-fix / CI / test PR (fix(hlog/sentry): capture original error to preserve stack trace #5–test(redislock): constructors, Health regression, guarded integration (0% → 18%) #25) and the before→after coverage table.
• Environment gotchas — the golangci-lint v1/v2 config mismatch, why CI pins golangci-lint v1.55.2 on Go 1.21 and the test job on Go 1.22, the whole-tree gofmt check, integration-test env vars, blocked SDK/WebFetch.
• Open v1 punch list — registry concurrency, LevelFromString panic, hurl status threshold, go mod tidy, version.go vs tag mismatch, session.go prototype, untested zap/mongo paths, the lint package-comment backlog.
• The phased v1 plan (Phases 0–5) + open decisions for the maintainer.
• Peer-framework research notes (Kratos / go-kit / go-micro / Uber Fx + Go module versioning) with sources.
• Architecture cheat-sheet of what lives in each package.

Docs-only; no code changes.

🤖 Generated with Claude Code

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