feat: moved branch scope detection to scripts

[RuiMiguel]

Description

#145

Multiple skills contain inline bash commands for detecting the current branch and base branch. These are deterministic operations that don't need LLM reasoning.

1. Detect base branch — checks for main, then master, then develop. Appears in:
   - rebase/SKILL.md (lines 26-28)
   - review/SKILL.md (lines 38-42)
   - create-branch/SKILL.md (line 29 — checks if current branch is one of these)
2. Detect review scope — review/SKILL.md (lines 30-56) runs ~6 bash commands to detect branch, base branch, changed files, uncommitted changes, and deduplicates.

Plan:

1. Create skills/shared/scripts/detect-base-branch.sh — outputs the default branch name, exits 1 if none found
2. Create skills/shared/scripts/detect-review-scope.sh — outputs current branch, base branch, and deduplicated changed files
3. Update rebase/SKILL.md — replace inline detection with script call
4. Update review/SKILL.md — replace multi-step scope detection with script call
5. Update create-branch/SKILL.md — replace inline base-branch list with script call
6. Add symlinks in each skill's directory so paths stay local

Scripts encapsulate existing bash logic. Skills still own all decision-making.

Type of Change

• New feature (feat)
• Bug fix (fix)
• Code refactor (refactor)
• Documentation (docs)
• CI change (ci)
• Chore (chore)

[ryzizub]

LGTM