docs: stop duplicating the language count in the Orbit Local section

[rajanpanth]

The Orbit Local section restates the supported-language count that already appears twice elsewhere in the project, and the three copies have drifted apart:

Location	Says
README.md, Orbit Local section	11+ languages
README.md, Orbit Remote section	11+ languages, then names 14 of them including Elixir
docs/source/indexed-data.md table	13 rows, no Elixir
crates/code-graph/src/v2/config/lang.rs	20 declared, including Scala, HCL, Swift, Lua, YAML and Zig

Rather than adding a fourth number to keep in sync, this points the Orbit Local blurb at the Orbit Remote section it is already deferring to:

It indexes the same languages as Orbit Remote.

One line, and nothing left in that sentence to go stale.

Note on the original scope of this PR. It was opened to change the Orbit Local count from 11+ to 13 to match the docs table. That was wrong, and I would rather say so than quietly reword it: main has since grown Elixir support (crates/code-graph/src/v2/langs/generic/elixir.rs, registered in config/lang.rs), so writing 13 there would have asserted a number that is too low and the diff would have dropped Elixir from the list in the Remote section. The docs table is the stale artefact, not the README. I have not touched the table here, since deciding which of the 20 declared languages belong in a table whose columns are "Definitions" and "Cross-file references" is a call for someone who knows which are full parsers and which are the generic DSL path.

[rajanpanth]

Rebased onto current main and changed what this PR does, so flagging it rather than leaving a silent force-push.

The original premise was wrong. I opened this to change 11+ languages to 13 in the Orbit Local section to match the table in docs/source/indexed-data.md. Since then main gained Elixir support (crates/code-graph/src/v2/langs/generic/elixir.rs, registered in config/lang.rs), and lang.rs now declares 20 languages in total. So 13 would have been too low, and the diff would also have removed Elixir from the list in the Remote section. The docs table is the stale one here, not the README.

The PR now drops the duplicated count from the Orbit Local blurb instead, so that sentence defers to the Remote section rather than carrying its own figure. Title and description updated to match.

Happy to close this if you would rather leave the wording as is.