fix(plugins): say what telemetry actually sends, and salt the hashes

The plugin README promises "anonymous usage events" and the telemetry module's
docstring says it sends only "salted hashes". Neither is true.

resolve_distinct_id() exchanges the API key for the account email and sends that
as the distinct_id on every event. Installing the plugin requires an API key, so
this is nearly every user. That is probably the behaviour we want — the Python
SDK and the CLI attribute the same way — but the description has to match it.

repo_hash and session_hash were unsalted SHA-256 cut to 16 hex characters.
repo.identity is a git remote URL, or `local:<absolute path>` when there is no
remote, which normally contains the account username. Sixteen unsalted hex
characters over that input space is enumerable, so the hash was not a privacy
control at all.

Salted per install, with the salt kept in the identity file. That preserves
every within-account join the analytics actually use and gives up only
cross-machine joins on the same repository, which nothing computes. Since the
distinct_id is already the email, the hash was never buying privacy from us —
only from whoever obtains the data later, which is exactly what the salt fixes.

Also corrects deepseek-plugin's README and source comment, which told readers
ZAPIER and STRANDS were already in the backend's KNOWN_EVENT_SOURCES allowlist.
Neither was.

Adds a Telemetry section to docs/integrations/claude-code.mdx, which had none.

Claude-Session: https://claude.ai/code/session_01C7tEmH86HAr7GoAAKCEHZb

docs/integrations/claude-code.mdx

@@ -172,6 +172,31 @@ claude plugin update mem0@mem0-plugins --scope user
 | Sidekick won't start | Must be in a Git repo. Check that your Claude Code version supports plugin agents and worktrees. |
 | Remove the plugin | `claude plugin uninstall mem0@mem0-plugins` |
 
+## Telemetry
+
+The plugin sends usage events (which hook ran, timing, result counts, failure
+types) so Mem0 can see what's used and what's breaking.
+
+These events are **not anonymous**. When an API key is configured, which
+installing the plugin requires, they are sent under your Mem0 account email,
+the same way the Python SDK and the CLI attribute theirs. Without a key they
+are sent under a random per-machine id.
+
+Each event carries the event name, the plugin version, the harness it ran in,
+your OS and Python version, timings, counts, and a coarse failure label.
+Repository and session identifiers are hashed with a random salt generated on
+your machine and never sent, so they cannot be linked back to a repository name
+or path.
+
+Prompts, memory text, queries, file paths, repository names, and API keys are
+never sent.
+
+Turn it off:
+
+```bash
+export MEM0_TELEMETRY=false
+```
+
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     Detailed MCP configuration for all clients