docs(memory-providers): fix Mnemosyne tool count, install symlink, and lifecycle phrasing

[AxDSan]

Follow-up review of NousResearch#34356. Four verified corrections sourced from the actual Mnemosyne codebase:

1. Tool count: 19 -> 26 — missed 7 tools: mnemosyne_remember_canonical, mnemosyne_recall_canonical, mnemosyne_shared_remember, mnemosyne_shared_recall, mnemosyne_shared_forget, mnemosyne_shared_stats, mnemosyne_triple_end. Verified from ALL_TOOL_SCHEMAS in hermes_memory_provider/__init__.py.

2. Install symlink was broken (blocker) — the original docs symlink into mnemosyne/ package's __init__.py, which does NOT contain register_memory_provider(). That entry point lives in the sibling package hermes_memory_provider/. A user following the original instructions would get "No memory provider plugins detected."

3. Removed hermes memory setup from install snippet — Mnemosyne is zero-config after setting memory.provider: mnemosyne. No interactive wizard needed.

4. Lifecycle phrasing — register is the CLI plugin entry point, not the provider contract method. The provider contract uses register_memory_provider. Clarified both.

Verification

Every claim confirmed against the live source (mnemosyne-memory, commit cf297d8):

python3 -c 'from hermes_memory_provider import ALL_TOOL_SCHEMAS; print(len(ALL_TOOL_SCHEMAS))'
26

grep -n 'def register_memory_provider\|def register' hermes_memory_provider/__init__.py
2602:def register_memory_provider(ctx):
2612:def register(ctx):