refactor: drop MAX_FILE_CHARS cap on --doc file size

It didn't actually guard what it claimed to: std::fs::read_to_string
loads the whole file into memory before truncation ever ran, so it
never prevented the OOM risk it was documented as protecting against
— it only capped how much of the already-fully-read text got chunked
afterward. Directory scanning is non-recursive and --doc is an
explicit opt-in, so an oversized file is on the caller; chunking
already handles arbitrarily long documents correctly. Can add a
pre-read fs::metadata size check back later if real usage shows a
need for it.

src/documents.rs

@@ -2,12 +2,6 @@ use rig::embeddings::{EmbedError, TextEmbedder};
 use std::path::{Path, PathBuf};
 use text_splitter::{Characters, TextSplitter};
 
-/// Safety valve against accidentally pointing `--doc` at a huge binary or
-/// log file — not a content limit. Real documents are chunked in full (see
-/// `CHUNK_CHARS` below), so nothing meaningful gets silently dropped short
-/// of this.
-const MAX_FILE_CHARS: usize = 2_000_000;
-
 /// Target chunk size handed to the embedding model: small enough that a
 /// handful of retrieved chunks stays well within a local model's context
 /// window, large enough to keep a paragraph or two of context in each one.
@@ -61,13 +55,7 @@ pub(crate) fn collect_documents(paths: &[PathBuf]) -> anyhow::Result<Vec<Documen
 
 fn push_document(path: &Path, splitter: &TextSplitter<Characters>, documents: &mut Vec<Document>) {
     match std::fs::read_to_string(path) {
-        Ok(mut text) => {
-            // Cheap upper bound on char count, so the vast majority of
-            // documents (well under the limit) skip the char-by-char walk
-            // entirely.
-            if text.len() > MAX_FILE_CHARS && text.chars().count() > MAX_FILE_CHARS {
-                text = text.chars().take(MAX_FILE_CHARS).collect();
-            }
+        Ok(text) => {
             let chunks: Vec<&str> = splitter.chunks(&text).collect();
             let total = chunks.len();
             let source = |i: usize| {