fix(mcp): refuse strict=true in compile tool, remove strict schema default

[Copilot]

The MCP compile tool had AddSchemaDefault(..., "strict", true), causing LLM clients to always pass strict: true even when not explicitly requested. This silently recompiled non-strict workflows with --strict, producing unwanted lock-file diffs (e.g. GH_AW_COMPILED_STRICT: "false" → "true", dropped Enforce strict mode policy step).

Changes

• Remove schema default: Drop AddSchemaDefault(compileSchema, "strict", true) — LLMs no longer receive a default: true hint for strict, so unspecified calls compile without --strict
• Refuse strict=true at runtime: Add an early guard that returns CodeInvalidParams when strict: true is passed, directing users to gh aw compile --strict
• Remove dead code: Drop the now-unreachable --strict flag append
• Update descriptions: Strict field and tool description updated to reflect the not-supported status
• Tests: Inverted the elicitation-defaults test to assert no strict default; added TestMCPServerUnit_CompileToolRejectsStrict; updated the integration test to expect an error on strict: true

// Before: schema default caused LLMs to always pass strict: true
AddSchemaDefault(compileSchema, "strict", true)

// After: no default; strict=true is refused at runtime
if args.Strict {
    return nil, nil, newMCPError(jsonrpc.CodeInvalidParams,
        "compile with strict=true is not supported via the MCP tool; use gh aw compile --strict for strict mode compilation", nil)
}

• Fixes [cli-tools-test] agenticworkflows compile MCP tool defaults to strict mode, causing unwanted lock-file diffs #49482