feat: decouple snapshot generation from publishing

[bdchatham]

Summary

Implements the merged design in docs/design-snapshot-publish-config.md (#107). Operators can now generate local Tendermint snapshots without also uploading them to S3, and the snapshot-config surface is shaped so future snapshot flavors slot in without renaming fields.

• Refactored SnapshotGenerationConfig to nest a TendermintSnapshotGenerationConfig sub-struct; added optional Publish struct whose presence enables S3 upload. Matches the existing StateSyncSource struct{} / SnapshotSource presence-as-toggle pattern already used in common_types.go.
• Re-wired the existing seictl TaskTypeSnapshotUpload sidecar task as a fire-and-forget plan task. Inserted into the init progression immediately before mark-ready only when publish is set. Restores controller-side plumbing that was deleted in feat: remove monitor task system #89 with the monitor-task subsystem, now as a plan task.
• Cross-field validation (empty snapshotGeneration, publish + keepRecent < 2) lives in each planner's Validate(node) hook with its own mode-prefixed error (fullNode: / archive:). No admission webhook introduced; no shared helper takes a mode parameter.
• Samples (pacific-1-snapshotter.yaml, pacific-1-state-syncer.yaml) updated to the new shape, preserving their prior publishing behavior.
• CRDs regenerated via make manifests generate; DeepCopy regenerated. No hand edits to generated files.

Shape of the new surface

# Generate 5 local snapshots + upload to S3 (previous default behavior)
snapshotGeneration:
  tendermint:
    keepRecent: 5
    publish: {}

# Generate 3 local snapshots, do NOT upload (new capability)
snapshotGeneration:
  tendermint:
    keepRecent: 3

# No snapshot generation
# (field omitted)

Verification

• make build — succeeds
• make lint — 0 issues
• make test — all packages pass
• Independent cross-review of the diff vs. the design doc: all 14 checks COMPATIBLE (type shape, planner overrides, validation shape & rules, plan-task wiring on both non-bootstrap and post-bootstrap paths, exclusion from the bootstrap Job's own sidecar, samples, tests, generated files)

Test plan

• Apply an updated sample SeiNode with publish: {} and observe snapshot-upload appearing in .status.plan between config-validate and mark-ready
• Apply the same sample with publish omitted and confirm snapshot-upload is NOT in the plan; confirm seid still writes snapshots to the data volume at the configured interval
• Apply a spec with publish: {} and keepRecent: 1 — expect the planner's Validate() to reject with a clear error mentioning the upload algorithm
• Apply snapshotGeneration: {} (empty) — expect the planner's Validate() to reject as a typo-shape
• Spot-check one existing snapshotter node: delete + recreate under the new shape; confirm the sidecar begins uploading after mark-ready
• Review generated CRD YAML in manifests/sei.io_seinodes.yaml and manifests/sei.io_seinodedeployments.yaml for the new nested shape

🤖 Generated with Claude Code