Push claw-wall messages into channel-memory

[mostlydev]

Summary

• add pod-level x-claw.channel-memory.service wiring for the channel-memory adapter
• inject a channel-memory bearer token plus /ingest URL into claw-wall
• push retained claw-wall messages from startup backfill, forward polling, and gap repair into channel-memory with stable identity and content hashes
• add a protected replay endpoint for retained raw messages and keep raw-window serving fail-open when ingest fails
• document the generic pod wiring in examples/channel-memory

Validation

• go test ./internal/pod -run 'TestParsePod(ExtractsChannelMemory|RejectsInvalidCapabilityConfig)'\n- go test ./cmd/claw -run 'TestInjectConversationWallWiresChannelMemory'\n- go test ./cmd/claw-wall -run 'Test(DiscordPollerPushesBackfillToChannelMemory|DiscordPollerPushesForwardPollToChannelMemory|DiscordPollerChannelMemoryFailureDoesNotBlockRawWindow|ChannelMemoryReplayRequiresAllowedChannels|LoadConfigReadsChannelMemoryConfig)'\n- go test ./examples/channel-memory\n- go test ./...\n- go vet ./...\n- git diff --check\n- go test -tags spike -v -run TestSpikeChannelBackfill -timeout 5m ./cmd/claw/...\n\nCloses claw-wall: push channel messages into channel-memory #266\nRefs Plan + ADR for channel-memory capability and digest-backed channel-awareness (issue #232 Phase 2) #262 channel-memory: add SQLite source-message adapter #265