feat(opencode): add isReadOnly and isDestructive flags to tool interface

[AndresCdo]

Issue for this PR

Closes #20296

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds optional isReadOnly and isDestructive metadata flags to the Tool.Def interface. These flags enable the permission system, auto-approval classifiers, and UI to make smarter decisions about tool behavior without analyzing tool internals at runtime.

Annotated 11 built-in tools:

Tool	Flag	Rationale
read	isReadOnly: true	Only reads file contents
glob	isReadOnly: true	Only matches file patterns
grep	isReadOnly: true	Only searches file contents
list	isReadOnly: true	Only lists directory contents
webfetch	isReadOnly: true	Only fetches URL content
codesearch	isReadOnly: true	Only queries external API
write	isDestructive: true	Creates/overwrites files
edit	isDestructive: true	Modifies file contents
apply_patch	isDestructive: true	Applies patches to files
multiedit	isDestructive: true	Multiple file modifications
todowrite	isReadOnly: false	Modifies session state

Tools not annotated: bash (dynamic — can be read-only or destructive depending on command), task, websearch, skill, lsp, plan_exit, plan_enter, question, invalid, batch — these have complex or context-dependent behavior.

How did you verify your code works?

• bun typecheck passes (zero errors in changed files)
• Changes are purely additive: optional fields with no behavioral change
• 12 files changed, +15 lines total
• No API changes, no breaking changes

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR