docs: add ACP and internal systems implementation guides

- add ACP user and developer docs covering setup, lifecycle, callbacks,
  permissions, tool rendering, and runtime behavior
- add developer guides for agent loop, provider runtime resolution,
  prompt assembly, context caching/compression, gateway internals,
  session storage, tools runtime, trajectories, and cron internals
- refresh architecture, quickstart, installation, CLI reference, and
  environments docs to link the new implementation pages and ACP support

website/docs/developer-guide/cron-internals.md

@@ -0,0 +1,56 @@
+---
+sidebar_position: 11
+title: "Cron Internals"
+description: "How Hermes stores, schedules, locks, and delivers cron jobs"
+---
+
+# Cron Internals
+
+Hermes cron support is implemented primarily in:
+
+- `cron/jobs.py`
+- `cron/scheduler.py`
+- `gateway/run.py`
+
+## Scheduling model
+
+Hermes supports:
+
+- one-shot delays
+- intervals
+- cron expressions
+- explicit timestamps
+
+## Job storage
+
+Cron jobs are stored in Hermes-managed local state with atomic save/update semantics.
+
+## Runtime behavior
+
+The scheduler:
+
+- loads jobs
+- computes due work
+- executes jobs in fresh agent sessions
+- handles repeat counters
+- updates next-run metadata
+
+In gateway mode, cron ticking is integrated into the long-running gateway loop.
+
+## Delivery model
+
+Cron jobs can deliver to:
+
+- origin chat
+- local files
+- platform home channels
+- explicit platform/chat IDs
+
+## Locking
+
+Hermes uses lock-based protections so concurrent cron ticks or overlapping scheduler processes do not corrupt job state.
+
+## Related docs
+
+- [Cron feature guide](../user-guide/features/cron.md)
+- [Gateway Internals](./gateway-internals.md)