Add reasoning effort control and selectable messages

[windzu]

Summary

• allow user and assistant message text to be selected and copied inside the Obsidian item view
• add a reasoning-effort control next to the conversation model picker
• populate effort choices dynamically from each Codex model's supportedReasoningEfforts
• persist explicit effort choices per conversation and forward them to Codex on every turn
• clear an incompatible explicit effort when the conversation model changes

Root cause

Message content did not override the non-selectable behavior inherited from Obsidian's application-style view shell. The model catalog integration also discarded supportedReasoningEfforts and defaultReasoningEffort, even though model/list already returned both fields, leaving the composer with model names only.

User impact

Users can select and copy rendered responses. They can also choose the reasoning level supported by the active Codex model; leaving the control on Default uses that model's advertised default.

Validation

• npm run typecheck
• npm test (70 tests passed)
• npm run build
• queried the installed Codex app-server model/list and verified model-specific effort catalogs
• deployed the exact build to the local development Vault and verified artifact hashes match

Screenshots

Not attached because the message-selection fix has no static visual delta and the effort menu is rendered by Obsidian's native Menu; the control was validated in the local development Vault.