fix(ruby): apply launchConfig.cwd to the debuggee spawn options (#320)

[debugmcpdev]

Fixes #320. Sibling of #318 (env, PR #321) — completes the family of spawn-time launch options for ruby.

Problem

cwd passed via dapLaunchArgs was silently dropped on the ruby launch path: with rdbg --open -c -- ruby <script> the debuggee starts at adapter-spawn time, so the cwd carried in the later DAP launch request is never applied and the debuggee inherits the proxy worker's working directory instead. The spawn layer already supported cwd (dap-proxy-adapter-manager.ts sets spawnOptions.cwd when provided) — nothing delivered the value to it.

Fix

Route launchConfig.cwd through the same channel as the #318 env fix:

• AdapterCommand gains an optional cwd field (packages/shared/src/interfaces/debug-adapter.ts), mirrored on AdapterSpawnPayload.adapterCommand.
• RubyDebugAdapter.buildAdapterCommand sets it from launchConfig.cwd.
• The ruby policy's spawn config passes it through (adapter-policy-ruby.ts); the AdapterSpawnConfig union already declared cwd?.

Optional field end to end — no other adapter or policy changes behavior (their debuggees get cwd via the DAP launch request as before). Attach mode untouched.

Tests

• Hard e2e (mcp-server-smoke-ruby.test.ts): launch fizzbuzz with dapLaunchArgs: { cwd: <examples/ruby> }, evaluate the working directory at a breakpoint. Red before the fix (debuggee sat in the repo root), green after. The expression evaluates only the path tail (Dir.pwd.split('/').last(2)) because the [FEATURE] Secret redaction + least-privilege variable inspection #237 redaction — on by default — masks home-rooted paths as <redacted:sensitive-name>.
• Unit: adapter command carries cwd (and stays undefined when unset); policy routes adapterCommand.cwd into the spawn config.
• Full ruby suite green (all 6 smoke e2e tests including [BUG] comprehensive e2e matrix: ruby get_output marker '1: 1' not captured mid-run (soft FAIL cell) #317/[BUG] ruby launch ignores launchConfig.env — user-provided env never reaches the debuggee #318's); validateAdapterCommand's error doc updated to mention the optional field; docs section extended to cover cwd alongside env.

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