fix(knowledge): keep leading indent of indented code blocks in chunks

[harsh-thakkar7]

What

Chunk building trimmed each section/paragraph with str.strip(), which removes the leading indentation of the first line of a 4-space indented code block:

## Setup

    def setup():      <- chunk stored as "def setup():"

The stored chunk and the AI prompt context both re-flowed the code as though the indentation never existed.

Fix

Trim surrounding blank lines instead of all whitespace (strip("\n").rstrip()), preserving interior indentation — in the section path, the paragraph-split path (large sections), and the prompt-context builder.

Tests

• tests/test_knowledge_logic.py: the first code line keeps its indent in the small-section path, the large-section (paragraph-split) path, and the prompt context.
• Full backend suite passes (472 tests). Ruff clean.

[petertzy]

Approved — this is a necessary correctness fix. Chunk construction and prompt-context generation now preserve the leading indentation required for indented Markdown code blocks, preventing code from being reflowed as prose.
I also fixed the remaining entry-point and post-frontmatter paths, where an initial indented code block could still lose its first-line indentation. The regression coverage now includes small sections, paragraph-split chunks, prompt context, Overview chunks, and frontmatter bodies. Backend tests (485 passed), frontend tests (94/94), Ruff, ESLint, and TypeScript checks all pass.