docs(clone): stronger usage example + table of contents

[ob-aion]

Summary

The Usage section only showed reads, which doesn't convey what a structural clone actually preserves. Replace it with a runnable example that demonstrates mutation isolation through a side-effecting method, then a direct, verified divergence from lodash.cloneDeep. Add a table of contents.

Changes

• Usage rewrite — three blocks: (1) mutate the copy via a class method, source untouched, prototype + Map survive; (2) lodash.cloneDeep flattens a getter to its clone-time value (stale total) and silently drops a non-enumerable key, where clone keeps both live; (3) freeze locking the graph recursively.
• TOC — ## Contents linking the top-level sections.

Accuracy

Every value in the example was verified empirically against the installed lodash.clonedeep and the built clone:

Check	clone	lodash.cloneDeep
getter stays live after array push	115	15 (frozen at clone time)
total descriptor has get	true	false
non-enumerable secret	'k-1'	undefined
instanceof / Map	preserved	also preserved (not claimed otherwise)

lodash keeps prototypes and native types; the example does not claim otherwise. It targets only the accessor and non-enumerable cases where the two genuinely diverge.

Test plan

• All example outputs reproduced via a scratch script against dist/ + lodash.clonedeep (script not committed)
• Markdown anchors verified for the TOC
• CI green on this PR

[ob-aion]

OK