Delete v1 distribution artifacts

[massive-value]

What to build

Remove the v1-era parallel distribution channels from the source tree as part of the v2 cutover. Delete:

• /plugins/wealthbox-crm/ (entire directory)
• /codex-skill/wealthbox-crm/ (entire directory)
• .claude-plugin/marketplace.json

The single source-of-truth skill template at src/wealthbox_tools/skills/wealthbox-crm/ remains the only copy. The marketplace listing on Anthropic's side is delisted manually on release day; this issue covers only the in-repo cleanup.

User stories: 25, 26.

Acceptance criteria

• /plugins/wealthbox-crm/ no longer exists in the repo
• /codex-skill/wealthbox-crm/ no longer exists in the repo
• .claude-plugin/marketplace.json no longer exists in the repo
• No remaining references to those paths in code, docs, or CI workflows
• pytest and ruff check src/ tests/ pass

Blocked by

None - can start immediately

[massive-value]

Deferred from PR #64 (now closed). Per Codex review on #64, deleting these in-repo artifacts breaks the still-shipped Claude install path because:

• .claude-plugin/marketplace.json is consumed by scripts/install.{sh,ps1} and the README (claude plugin marketplace add).
• plugins/wealthbox-crm/ is the source dir referenced by marketplace.json.
• .codex-plugin/plugin.json references ./codex-skill, so deleting the codex-skill dir orphans that manifest.

Sequencing: this issue should land after #42 (install.sh binary rewrite), #43 (install.ps1 parity), and #55 (README v2 rework drops the marketplace install path). Once those are in, the cascade is unconsumed and the deletions are safe.

Adding native blockedBy on the GitHub side.