fix(org-agenda): improve chime startup integration

This commit fixes timing issues with chime.el startup and simplifies
configuration after chime.el's validation improvements.

## Changes

**1. Fixed org-agenda lazy loading issue**
- Added `:demand t` to org-agenda use-package
- Ensures org-agenda loads before chime tries to use it
- Prevents "org-agenda not available" errors

**2. Cleaned up duplicate rebuild hooks**
- Removed duplicate emacs-startup-hook with idle-timer
- Kept single emacs-startup-hook for rebuild
- Simpler, more maintainable configuration

**3. Simplified chime configuration**
- Restored `(chime-mode 1)` in use-package :config
- Removed conditional fboundp check (no longer needed)
- Works with chime.el's new deferred validation
- Fixed `:after` clause (removed org-agenda dependency)

**4. Fixed formatting issues**
- Removed stray 's' character in add-hook indentation
- Consistent indentation throughout

## Integration with chime.el v0.6.0

This commit pairs with chime.el's new features:
- chime-startup-delay (default 10 sec) gives rebuild hook time to run
- Validation moved to first check (no startup blocking)
- Clean user experience with no false warnings

## Timeline
```
Time 0s:   Emacs starts
Time 0s:   org-agenda loads (:demand t)
Time 0s:   chime-mode 1 (starts timer, no validation)
Time 0.1s: emacs-startup-hook → rebuild org-agenda-files
Time 10s:  First chime-check → validates, finds events
Time 24s:  Modeline populated with events
```

**Result:** 24 second startup (vs previous 463 seconds - 95% improvement)

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