fix: remove duplicate-word typos in error message, prompt, and test label

[devteamaegis]

Summary

Three small duplicated-word typos, each one self-contained:

File:line	Fix	Why it matters
`core/llm/index.ts:459`	`use the the Codestral API` → `use the Codestral API`	User-facing error message. The sibling branch one line up (line 455) already reads "use the Mistral API" correctly, so this fixes an asymmetry users hit when their API-key/apiBase combination is wrong.
`core/commands/slash/built-in-legacy/draftIssue.ts:10`	`If the the user request` → `If the user request`	Part of the LLM prompt for the draft-issue slash command — gets sent to the model verbatim.
`core/autocomplete/context/root-path-context/test/testCases/typescript.ts:301`	`method_declaration with with generic params` → `method_declaration with generic params`	`nodeType` label only — checked the file: `nodeType` is descriptive metadata, never matched against parsed source. Sibling entries on lines 252/262/271/280 follow the singular-`with` pattern.

Diff is exactly 3 lines.

Novelty

`gh search prs --repo continuedev/continue` against `use the the`, `the the user`, and `with with generic` all return empty. The only open typo PR (#12062) fixes a different message in another file — no overlap.

Test plan

• `grep -rn "the the \| with with " --include='*.ts' core/` (excluding node_modules) returns no matches after the fix.
• The error message in `core/llm/index.ts` continues to be the same shape as its sibling branch on line 455.

---

Summary by cubic

Fixed duplicate-word typos ("the the", "with with") in a user-facing error message, the draft-issue LLM prompt, and a test label to improve clarity and consistency.

^{Written for commit 274510e. Summary will update on new commits. Review in cubic}

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}

[devteamaegis]

I have read the CLA Document and I hereby sign the CLA