feat(install): add IBM Bob platform support (#1725)

[Animesh0764]

Closes #1725

Adds IBM Bob (AI IDE/CLI) as a supported platform.

What this adds

• graphify install --platform bob — installs the skill to Bob's global skills dir (~/.bob/skills/graphify/SKILL.md)
• graphify bob install — project-scoped: skill at .bob/skills/graphify/ + an always-on rules file at .bob/rules/graphify.md
• graphify bob uninstall, graphify install --project --platform bob, and the all-platform graphify uninstall all handle Bob; graphify uninstall --project picks it up automatically via _PLATFORM_CONFIG

Design notes

• Rides kiro's skill bundle (skill-kiro.md + skill_refs: "kiro"), same precedent as hermes→claw and trae-cn→trae: Bob uses the same
  agent-tool dispatch and the kiro body contains no host-specific wording, so no skillgen changes or new rendered artifacts are needed.
• Rules file is a hand-written constant (_BOB_RULES, Devin-style) rather than a skillgen always_on/ fragment — the always-on roundtrip
  validator is pinned to the frozen v8 baseline, which new blocks can't join.
• Rules are project-only, matching the existing convention (kiro/devin/cursor): global install copies only the skill. Per Bob's docs,
  .bob/rules/ files are loaded alphabetically as always-on context, and Bob has no PreToolUse-hook equivalent, so the rules file is the always-on
  mechanism.
• Paths verified against Bob's docs (bob.ibm.com/docs/ide): skills at .bob/skills/<name>/SKILL.md (project) / ~/.bob/skills/ (global), SKILL.md
  frontmatter needs only name + description, sidecar files are supported — so the split references/ bundle works as-is.

Testing

• 15 new tests in tests/test_bob.py (user/project scope install, references sidecar, rules content, idempotency, uninstall, config sanity, help
  text) — all pass
• Bob is automatically covered by the parametrized suites (test_install_roundtrip, test_install_references, test_wheel_packaging) — all pass
• Full suite: 3109 passed; the 35 failures are pre-existing Windows-host artifacts (symlink tests need elevation, cp1252/path-separator assumptions),
  verified identical on a clean tree — none related to this change
• Manually verified end-to-end: graphify bob install lays down SKILL.md + 8 references + version stamp + rules file; graphify bob uninstall
  removes everything