docs: improve docs and add diagrams

[frrist]

Docs-only refresh — the overdue post-migration doc pass, plus new as-built diagrams.

• Rewrites the four documents that still described the pre-July architecture (two-plane log, standalone mode, login CLI): DESIGN_NOTES.md, README.md, logstore/README.md (now covers the per-bucket Manager), and CLAUDE.md (package map, config keys, seams, dependency list).
• Refreshes docs/architecture.md and adds docs/diagrams.md — 15 as-built diagrams spanning system context, the package/seam map, the body-blob vs catalog block routes, the PutObject/GetObject/multipart flows, blob and session lifecycles, per-key version storage, catalog GC, principals/proof stores and request authorization, the migrated Postgres schema, and DeleteBucket teardown order.
• Comment-only touch-ups in module.go, registry/postgres.go, server.go; no behavior change anywhere in the diff.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Docs-only refresh aligning repository documentation with the current (post-migration) ingot architecture, including a new as-built diagram set intended to stay in sync with the code.

Changes:

• Rewrites/updates core docs to reflect the current bucket-segregated catalog log, blob upload flow, and hilt-owned tenancy/auth.
• Adds docs/diagrams.md with an indexed set of as-built diagrams (with per-diagram “Sources” footers and a package-to-diagram map).
• Updates/clarifies a small number of in-code comments to match the current architecture.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
server.go	Updates the flush-function comment to describe the per-bucket catalog ship path.
registry/postgres.go	Updates type-level documentation to reflect hilt-owned bucket authority and local SQL-only bucket rows.
README.md	Refreshes high-level architecture overview and running instructions; adds pointers to architecture + diagrams docs.
module.go	Updates package/module doc comment to match the current body-vs-catalog split and seams.
logstore/README.md	Rewrites logstore docs to reflect the per-bucket catalog-only log and its lifecycle/diagrams.
docs/s3-versioning.md	Adds a cross-link to the relevant diagram for the version storage shape.
docs/diagrams.md	New as-built diagram set + index and maintenance mapping.
docs/architecture.md	Updates target-architecture doc references and refreshes schema appendix text to match current implementation.
DESIGN_NOTES.md	Rewrites “as-operated-today” description to match current runtime/auth/shipping behavior and known gaps.
CLAUDE.md	Updates repo working notes (package map, seams, config keys, testing, diagram maintenance rule).

Suppressed comments (1)

logstore/README.md:193

• ManagerConfig is not declared in config.go (it lives in manager.go). Keeping it listed here makes the table inaccurate.

| `config.go` | `Config`, `ManagerConfig`, `PlaneConfig`, `FlushFunc` |

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