feat(watch)!: stream RustFS object notifications

[cxymds]

Closes rustfs/backlog#1374

Background and user impact

rc had no equivalent to mc watch. Users could not observe RustFS object creation, access, removal, version, or delete-marker activity from the CLI without polling.

Solution

• Adds typed streaming notification contracts to rc-core.
• Adds a SigV4-signed RustFS ListenNotification transport with incremental, bounded JSON-line decoding.
• Adds rc watch ALIAS[/BUCKET] with mc-compatible event shorthands, prefix/suffix filters, compact schema-v3 JSON Lines, human output, quiet mode, reconnects, and Ctrl-C handling.
• Advertises listen_notification only for the exact known RustFS 1.0.0-beta.10 release family while allowing undeclared future servers to answer authoritatively.
• Extends output schema v3 additively with watch source and delete-marker fields.

Review resolution

This PR supersedes #273 after its deleted base branch made reopening impossible.

• Replaces infallible streaming println! paths with fallible stdout writers.
• Treats stdout BrokenPipe as a clean watch termination with exit code 0, covering head, grep -m1, and closed pager pipelines without panic or spurious stderr.
• Preserves non-BrokenPipe stdout failures as ordinary I/O errors.
• Resets the reconnect budget after every successfully received event or keepalive, so --reconnect-attempts counts consecutive failures rather than lifetime disconnects.
• Adds regression tests for writer EPIPE, clean loop termination, and failure → healthy frame → disconnect → successful reconnect.
• Keeps malformed event frames fatal as an explicit integrity policy: the decoder does not silently discard a possibly corrupted notification.

BREAKING protected-file process

BREAKING: this PR adds a public command contract under the protected docs/reference/rc/ tree. The behavior is additive: no existing command, flag, exit code, configuration schema, or v1/v2 output contract changes. New watch consumers should read one schema-v3 JSON object per line and tolerate optional delete_marker and source fields. Transport keepalives are consumed without emitting output records.

Validation

• cargo fmt --all --check: passed.
• cargo clippy --workspace -- -D warnings: passed with zero warnings.
• cargo test --workspace: passed.
• Watch, formatter EPIPE, output-v3 schema, capability, help-contract, launcher, ops, and replication focused tests: passed after semantic integration with latest main.
• Compatibility script unit tests and repository consistency check: passed.
• git diff --check: passed.

[cxymds]

This PR supersedes #273 and carries all prior review fixes. The BrokenPipe path now terminates cleanly without panic, the reconnect counter resets after healthy frames, and both behaviors have regression coverage. The branch is integrated with latest main and the mandatory full workspace validation passes. Please re-review the migrated changes.