fix(dolt): exit 0 when push/pull finds no remote configured

[sjsyrek]

Summary

Fixes #3031. bd dolt push and bd dolt pull exit 1 when no Dolt remote is configured, causing agent session-close protocols to error out. This changes both commands to exit 0 with an informational message when the error is specifically "remote not found", since the absence of a remote is a valid configuration — not a failure.

Changes Made

• Added printNoRemoteGuidance() helper in cmd/bd/dolt.go — prints the existing "no remote" guidance to stdout (not stderr) and returns without error. Replaces the duplicated guidance blocks in push and pull.
• Changed bd dolt push exit behavior — when isRemoteNotFoundErr() is true, calls printNoRemoteGuidance() and returns (exit 0) instead of os.Exit(1). Other errors (diverged history, connection failures) still exit 1.
• Changed bd dolt pull exit behavior — same treatment: graceful exit 0 on remote-not-found, error exit on everything else.
• Deduplicated push error handling — the force-push and regular-push branches had identical 15-line "no remote" blocks; now both go through a single error-handling path.
• Added TestPrintNoRemoteGuidance — verifies the guidance mentions "No remote is configured", "skipping", and how to add a remote.

Backward Compatibility

✅ No behavioral change for configured remotes: push/pull with a valid remote work exactly as before
✅ No behavioral change for other errors: diverged history, connection failures, auth errors still exit 1
✅ Agents benefit immediately: session close protocols that call bd dolt push will no longer fail on fresh workspaces

Technical Details

The key behavioral changes:

Scenario	Before	After
bd dolt push (no remote)	stderr + exit 1	stdout + exit 0
bd dolt pull (no remote)	stderr + exit 1	stdout + exit 0
bd dolt push (diverged)	stderr + exit 1	stderr + exit 1 (unchanged)
bd dolt push (auth fail)	stderr + exit 1	stderr + exit 1 (unchanged)

The guidance text is written to stdout (not stderr) because it's informational, not an error condition.

Size: Small ✓

Two-file change with a net reduction in code (deduplication removes ~20 lines of copy-pasted guidance).

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