mbproxy/docs: split deep docs into focused PascalCase files per StyleGuide

Adds 11 topic-focused docs under docs/{Architecture,Features,Operations,Reference,Testing}/
and links them from README.md's new "Detailed documentation" section. Existing
top-level docs (design.md, kpi.md, operations.md) remain as canonical landings.

Architecture/
  - Overview.md         (150 lines) — listener topology, request flow, per-PLC isolation
  - ConnectionModel.md  (247 lines) — TxId multiplexer, watchdog, disconnect cascade
  - ReadCoalescing.md   (243 lines) — in-flight FC03/04 dedup via InFlightByKeyMap
  - ResponseCache.md    (398 lines) — opt-in per-tag TTL cache + range-overlap invalidation

Features/
  - BcdRewriting.md     (252 lines) — codec, CDAB, FC scope, partial-overlap policy
  - HotReload.md        (189 lines) — IOptionsMonitor + per-change-kind reconcile rules

Operations/
  - Configuration.md    (422 lines) — every Mbproxy:* option + validation rules
  - StatusPage.md       (334 lines) — admin endpoint surface, every JSON field
  - Troubleshooting.md  (364 lines) — diagnosis playbook keyed to log events

Reference/
  - LogEvents.md        (499 lines) — 28 events across 7 categories, grep-verified

Testing/
  - Simulator.md        (235 lines) — pymodbus fixture, skip policy, 3.13 framer quirk

Each doc was written by a dedicated agent against the StyleGuide.md rules with
a per-doc phase gate (PascalCase filename, H1 Title Case, code-fence language
tags, Related Documentation section with >=3 relative links, real type names
verified against src/). Cross-references between docs use relative paths;
all 18 README->docs links and all sibling links resolve.

Known follow-up: docs/design.md lines 215-251 are stale on two log-event
property templates (config.reload.applied and config.reload.rejected) and
mention LogContext.PushProperty scoping that isn't actually used. Reference/
LogEvents.md is now the authoritative event catalog and source-of-truth.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mbproxy/README.md

@@ -31,6 +31,36 @@ DL260/                DL205/DL260 reference material and pymodbus simulator prof
 | pymodbus simulator profile (register seeds for E2E tests) | [`DL260/dl205.json`](DL260/dl205.json) |
 | Agent-oriented coding guide (architecture bullets, device quirks, phase context) | [`CLAUDE.md`](CLAUDE.md) |
 
+## Detailed documentation
+
+The `docs/` tree is organized by topic. Start with [`docs/design.md`](docs/design.md) for the canonical end-to-end design; jump to the focused pages below when you need depth on one area.
+
+### Architecture
+
+- [`Architecture/Overview.md`](docs/Architecture/Overview.md) — Listener topology, request flow, per-PLC isolation.
+- [`Architecture/ConnectionModel.md`](docs/Architecture/ConnectionModel.md) — Single backend connection per PLC, TxId multiplexing, request-timeout watchdog, disconnect cascade.
+- [`Architecture/ReadCoalescing.md`](docs/Architecture/ReadCoalescing.md) — In-flight FC03/FC04 deduplication via `InFlightByKeyMap`.
+- [`Architecture/ResponseCache.md`](docs/Architecture/ResponseCache.md) — Opt-in per-tag response cache with bounded operator-configured staleness.
+
+### Features
+
+- [`Features/BcdRewriting.md`](docs/Features/BcdRewriting.md) — BCD codec, CDAB word order, FC03/04/06/16 scope, partial-overlap policy.
+- [`Features/HotReload.md`](docs/Features/HotReload.md) — `IOptionsMonitor`-driven config reload with per-change-kind reconcile rules.
+
+### Operations
+
+- [`Operations/Configuration.md`](docs/Operations/Configuration.md) — Full `appsettings.json` reference: every `Mbproxy:*` key, default, and validation rule.
+- [`Operations/StatusPage.md`](docs/Operations/StatusPage.md) — Admin endpoint surface (`/`, `/status.json`) with every JSON field documented.
+- [`Operations/Troubleshooting.md`](docs/Operations/Troubleshooting.md) — Diagnosis playbook keyed to log events and status counters.
+
+### Reference
+
+- [`Reference/LogEvents.md`](docs/Reference/LogEvents.md) — Stable `mbproxy.*` event catalog (28 events across 7 categories).
+
+### Testing
+
+- [`Testing/Simulator.md`](docs/Testing/Simulator.md) — pymodbus DL205 fixture, skip policy, and the load-bearing pymodbus 3.13 framer quirk.
+
 ## Build and run
 
 **Build (Debug, multi-file — fast for iteration):**