chore: prepare release 0.7.4

[steipete]

Summary

• finalize the 0.7.4 changelog date and wording
• update Linux package examples to the 0.7.4 release URLs

Verification

• GOWORK=off go test ./...
• GOWORK=off go vet ./...
• make generate-sqlc with clean generated diff
• goreleaser check
• goreleaser release --snapshot --clean --skip=publish
• source-blind nullable-message CLI contract: passed
• structured Codex autoreview of the final functional commit: clean

[clawsweeper]

ClawSweeper status: review started.

I am starting a fresh review of this pull request: chore: prepare release 0.7.4 This is item 1/1 in the current shard. Shard 0/1.

This placeholder means the worker is alive and reading the current context. I will edit this same comment with the actual review when the claws are done clicking.

Crustacean status: shell secured, claws on keyboard, evidence pebbles being sorted.