fix: add tiktoken as a direct dependency

[licat2023]

Problem

On a fresh install (3.1.13), the plugin silently fails to load: no /dcp or /dcp-compress commands, no compress tool, no prune notifications, and no debug logs are written even with "debug": true.

Root cause

@anthropic-ai/tokenizer does require("tiktoken/lite"), but tiktoken is only a transitive dependency. opencode's plugin installer does not always install it into the plugin cache (~/.cache/opencode/packages/@tarquinen/opencode-dcp@latest/node_modules), so importing the plugin entry throws:

Cannot find module 'tiktoken/lite' from '...@anthropic-ai/tokenizer/dist/cjs/index.js'

opencode catches this and silently drops the whole plugin, so nothing is surfaced to the user.

Fix

Promote tiktoken to a direct dependency. Direct dependencies are installed reliably by opencode's installer; the one that went missing here was a child of @anthropic-ai/tokenizer. tiktoken was already present in package-lock.json as a transitive dep (1.0.22), so this only adds the top-level declaration — no version change, no new resolution.

Verification

Reproduced the broken import, applied the equivalent of this change to the installed cache, then re-imported:

bun -e "await import('.../dist/index.js')"  # before: IMPORT ERROR: Cannot find module 'tiktoken/lite'
                                            # after:  OK

After the fix, restarting opencode exposes /dcp + /dcp-compress and DCP debug logs are written as expected.

Closes #575