fix(ai-controller): add 2000 character max-length guard on queryBuilder prompt

[aaniya22]

Closes #247

Problem

The queryBuilder controller validated that prompt was a non-empty
string but applied no upper-bound limit. This allowed arbitrarily large
prompts to be forwarded directly to the AI service, consuming unbounded
token quota per request.

Fix

Added a length check on safePrompt after trimming. Prompts exceeding
2000 characters are rejected with HTTP 400 before any AI service call
is made.

Changes

• apps/dashboard-api/src/controllers/ai.controller.js: added max-length
  guard in queryBuilder after the empty-string check

Summary by CodeRabbit

• Bug Fixes
  • Added validation to enforce a 2000-character limit on prompts. Requests exceeding this limit will now return an error.

[coderabbitai]

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 07f077f9-44e7-4520-b922-6e14bc8acd32

📥 Commits

Reviewing files that changed from the base of the PR and between 508dd3b and 6bed995.

📒 Files selected for processing (1)

• apps/dashboard-api/src/controllers/ai.controller.js

📝 Walkthrough

Walkthrough

The AI query builder controller now enforces a 2000-character maximum length on the prompt input. Requests exceeding this limit are rejected with HTTP 400 before forwarding to the Python service, preventing unbounded token consumption.

Changes

Prompt Length Constraint

Layer / File(s)	Summary
Prompt length validation apps/dashboard-api/src/controllers/ai.controller.js	The queryBuilder controller validates that the trimmed prompt does not exceed 2000 characters and throws a 400 AppError if the limit is exceeded, before any forwarding to the Python service occurs.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A prompt too long? No more, no more!
With 2000 chars, we've set the floor.
Tokens won't flee in a boundless spree—
Just right-sized words, wild and free!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: adding a 2000-character max-length validation guard to the AI controller's queryBuilder prompt parameter.
Linked Issues check	✅ Passed	The code changes fully address all objectives from issue #247: trimming is implemented, max-length validation of 2000 characters is enforced, and HTTP 400 errors are returned before any AI service call.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the stated objective of adding max-length validation to the queryBuilder prompt parameter with no unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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