[UX] `apc collect` has no `--dry-run` flag (asymmetric with `sync`)

[FZ2000]

Problem

apc sync has a --dry-run flag, but apc collect does not. This creates an asymmetry in the core workflow:

• You can preview what sync would write ✓
• You cannot preview what collect would extract ✗

Before running apc collect for the first time — especially when you have configs spread across multiple tools — it would be valuable to see:

• Which tools would be scanned
• How many skills/MCP servers/memory entries exist in each
• What conflicts would need resolution

Without --dry-run, users must commit to the full scan and then deal with conflict resolution interactively, with no way to back out cleanly.

Suggested Fix

Add --dry-run to apc collect:

apc collect --dry-run

Output:

  Scan Results (dry-run — cache not updated)
  ───────────────────────────────────────────
  Tool            Skills  MCP Servers  Memory
  claude-code          8            3       1
  cursor               2            2       0
  ─────────────────────────────────────────
  Total               10            5       1

  ⚠ Memory conflict: 1 tool has memory files (claude-code)

  Run without --dry-run to collect and merge.