Route commands and aggregates through Chronicle event source definitions

[einari]

Commands and aggregates can now route their events through a Chronicle event source definition and stream instead of free-form strings. The string decorators keep working.

Added

• @eventSourceDefinition(Source, 'Stream') for commands and aggregate roots (class, name, or a function returning the class for circular imports). Each event records its definition, and Chronicle derives the concurrency scope from the definition when no explicit scope or flags are set. Requires @cratis/chronicle 6.49.0 or later; older SDKs keep string routing and fail with a clear message only when a definition is selected. See Event source definitions. (part of Definition-based command and aggregate event source routing #181)
• Startup validation: building the application fails for a definition that is not an @eventSource class, an unknown name, a stream the definition does not declare, or string routing that contradicts the definition. (part of Definition-based command and aggregate event source routing #181)
• Per-event eventSource and eventStream on eventForEventSourceId replace the command's source and stream as a unit, and a raw per-event source or stream type wins over the command's definition. (part of Definition-based command and aggregate event source routing #181)
• defineChronicleCommand accepts an optional eventSource reference. (part of Definition-based command and aggregate event source routing #181)
• Aggregates declaring a definition are rehydrated and guarded only for that source and stream. (part of Definition-based command and aggregate event source routing #181)
• ChronicleArtifacts.eventSources exposes the discovered definitions to the Chronicle client.

Changed

• Development and sample dependencies move to @cratis/chronicle 6.49.0; the peer floor stays ^6.29.0.

[einari]

Checklist (reviewer-facing; verified locally on feature/registered-event-source-routing):

• @eventSourceDefinition for commands and aggregates; startup validation; per-event unit replacement; raw override wins; definition concurrency only without explicit scope or flags
• Specs: command, aggregate, nested transaction, mixed override, concurrency flags, older store, legacy string routing (full yarn test: 1199 files, 3471 specs pass)
• yarn build, check:declarations, check:consumers, check:chronicle-peer-floor (loads against SDK 6.29.0), typecheck, lint, docs:lint, docs:snippets, docs:examples, set-version --check
• Live kernel: ARC_CHRONICLE_TEST_SUITE=event-source-routing bash Source/Chronicle/run-integration.sh against cratis/chronicle:19.30.0-development on port 18800 (4/4 pass, including the native fail-closed guard)
• Screenplay grammar/generation: out of scope (owner-managed)
• Independent review, CI

Part of #181 and Cratis/Arc#2987; neither is closed by this PR.

[einari]

Independent review (head a745d42): no blocking defects. Added a clear diagnostic and spec for event source thunks that return neither a class nor a name. Verified: full suite 1200 files/3475 specs, build/typecheck/lint/consumers/declarations/docs, peer-floor, runtime load against real @cratis/chronicle 6.29.0 (string routing works, definition use fails with the 6.49.0 message), live suites against isolated kernel 18800: existing 4/4 and event-source-routing 4/4.