docs: update for encrypt-by-default CLI

Update README.md, api.md, and error hints to reflect:
- encryption is now default (no -e flag needed)
- use -E/--no-encrypt to disable
- file path shortcut (fpaste file.txt)

documentation/api.md

@@ -558,7 +558,7 @@ export FLASKPASTE_MIN_ENTROPY_SIZE=256 # Only check content >= this size (defaul
 **Caveats:**
 - Small data is exempt (configurable via `MIN_ENTROPY_SIZE`, default 256 bytes)
 - Compressed data (gzip, zip) also has high entropy — not distinguishable from encrypted
-- This is a heuristic, not cryptographic proof of encryption
+- This is a heuristic, not cryptographic proof of encryption
 
 **Recommended thresholds:**
 | Threshold | Effect |
@@ -597,7 +597,7 @@ export FLASKPASTE_REQUIRE_BINARY=1  # Reject recognizable formats (0=disabled)
 **Detected formats:**
 - `text/plain` (valid UTF-8 text)
 - `image/png`, `image/jpeg`, `image/gif`, `image/webp`
-- `application/pdf`, `application/zip`, `application/gzip`
+- `application/pdf`, `application/zip`, `application/gzip`
 
 **vs Entropy enforcement:**
 | Method | Detects | False positives |