CLI: Add --quiet flag to suppress non-data output

[titouanmathis]

Context

Agents and scripts piping CLI output need clean data without spinners, success messages, or decorative output mixed in. Currently, human-format output includes spinners on stderr and emoji-prefixed status messages that make parsing unreliable.

Proposal

Add --quiet / -q global flag that:

1. Suppresses spinners entirely (no progress indicators on stderr)
2. Suppresses status messages (no ✓ Time entry created, no ✗ Error)
3. Prints only the data to stdout (the resource payload or formatted list)
4. Errors still go to stderr with just the message (no emoji, no hints)

Example

# Normal
$ productive time add --service 123 --time 480
✓ Time entry created
ID: 99999
Date: 2026-03-24
Duration: 8h 0m

# Quiet
$ productive time add --service 123 --time 480 --quiet
99999

# Quiet + JSON (cleanest for piping)
$ productive time add --service 123 --time 480 --quiet --format json
{"id":"99999","date":"2026-03-24","time":480}

Interaction with --format json

--format json already avoids spinners and emojis, but still wraps output in status objects ({"status": "success", ...}). With --quiet --format json, output should be just the raw resource data.

Implementation

• Add quiet to CommandContext
• Spinner factory returns no-op when quiet
• OutputFormatter methods become no-ops for status/success/warning/info when quiet
• Only output() still writes to stdout