feat: Add timing and QUIET mode to Makefile

[angerman]

Summary

• Add timing information for build phases (cabal, stage1, stage2, bindist, test)
• Add QUIET=1 mode to suppress output unless there's an error
• Show timing summary at end of build (even on failure)
• Save timing data to _build/timing/summary.txt
• Enable QUIET=1 in devx CI workflow

Usage

make                  # Normal build with timing summary at end
make QUIET=1          # Quiet build - output only on error
make timing-summary   # Show timing summary only

Example Output

+------------------+---------------+--------+
| Phase            | Duration      | Status |
+------------------+---------------+--------+
| cabal            |        2m 15s | OK     |
| stage1           |       45m 10s | OK     |
| stage2           |     1h 24m 5s | OK     |
| bindist          |        1m 12s | OK     |
+------------------+---------------+--------+
| TOTAL            |    2h 12m 42s |        |
+------------------+---------------+--------+

Test plan

• Run make and verify timing summary appears at end
• Run make QUIET=1 and verify output is suppressed
• Verify logs are stored in _build/logs/
• Verify timing data is saved to _build/timing/summary.txt

[angerman]

This should only be merged after #117 is merged. But before #118 is merged. So that we can get the timing comparison between non, and minimal stage1.