feat(blocks): Implement Text Encode block (#11857)

## Summary
Implements a `TextEncoderBlock` that encodes plain text into escape
sequences (the reverse of `TextDecoderBlock`).

## Changes

### Block Implementation
- Added `encoder_block.py` with `TextEncoderBlock` in
`autogpt_platform/backend/backend/blocks/`
- Uses `codecs.encode(text, "unicode_escape").decode("utf-8")` for
encoding
- Mirrors the structure and patterns of the existing `TextDecoderBlock`
- Categorised as `BlockCategory.TEXT`

### Documentation
- Added Text Encoder section to
`docs/integrations/block-integrations/text.md` (the auto-generated docs
file for TEXT category blocks)
- Expanded "How it works" with technical details on the encoding method,
validation, and edge cases
- Added 3 structured use cases per docs guidelines: JSON payload
preparation, Config/ENV generation, Snapshot fixtures
- Added Text Encoder to the overview table in
`docs/integrations/README.md`
- Removed standalone `encoder_block.md` (TEXT category blocks belong in
`text.md` per `CATEGORY_FILE_MAP` in `generate_block_docs.py`)

### Documentation Formatting (CodeRabbit feedback)
- Added blank lines around markdown tables (MD058)
- Added `text` language tags to fenced code blocks (MD040)
- Restructured use case section with bold headings per coding guidelines

## How Docs Were Synced
The `check-docs-sync` CI job runs `poetry run python
scripts/generate_block_docs.py --check` which expects blocks to be
documented in category-grouped files. Since `TextEncoderBlock` uses
`BlockCategory.TEXT`, the `CATEGORY_FILE_MAP` maps it to `text.md` — not
a standalone file. The block entry was added to `text.md` following the
exact format used by the generator (with `<!-- MANUAL -->` markers for
hand-written sections).

## Related Issue
Fixes #11111

---------

Co-authored-by: Otto <otto@agpt.co>
Co-authored-by: lif <19658300+majiayu000@users.noreply.github.com>
Co-authored-by: Aryan Kaul <134673289+aryancodes1@users.noreply.github.com>
Co-authored-by: Nicholas Tindle <nicholas.tindle@agpt.co>
Co-authored-by: Nick Tindle <nick@ntindle.com>

docs/integrations/README.md

@@ -192,6 +192,7 @@ Below is a comprehensive list of all available blocks, categorized by their prim
 | [Get Current Time](block-integrations/text.md#get-current-time) | This block outputs the current time |
 | [Match Text Pattern](block-integrations/text.md#match-text-pattern) | Matches text against a regex pattern and forwards data to positive or negative output based on the match |
 | [Text Decoder](block-integrations/text.md#text-decoder) | Decodes a string containing escape sequences into actual text |
+| [Text Encoder](block-integrations/text.md#text-encoder) | Encodes a string by converting special characters into escape sequences |
 | [Text Replace](block-integrations/text.md#text-replace) | This block is used to replace a text with a new text |
 | [Text Split](block-integrations/text.md#text-split) | This block is used to split a text into a list of strings |
 | [Word Character Count](block-integrations/text.md#word-character-count) | Counts the number of words and characters in a given text |

docs/integrations/block-integrations/text.md

@@ -380,6 +380,42 @@ This is useful when working with data from APIs or files where escape sequences
 
 ---
 
+## Text Encoder
+
+### What it is
+Encodes a string by converting special characters into escape sequences
+
+### How it works
+<!-- MANUAL: how_it_works -->
+The Text Encoder takes the input string and applies Python's `unicode_escape` encoding (equivalent to `codecs.encode(text, "unicode_escape").decode("utf-8")`) to transform special characters like newlines, tabs, and backslashes into their escaped forms.
+
+The block relies on the input schema to ensure the value is a string; non-string inputs are rejected by validation, and any encoding failures surface as block errors. Non-ASCII characters are emitted as `\uXXXX` sequences, which is useful for ASCII-only payloads.
+<!-- END MANUAL -->
+
+### Inputs
+
+| Input | Description | Type | Required |
+|-------|-------------|------|----------|
+| text | A string containing special characters to be encoded | str | Yes |
+
+### Outputs
+
+| Output | Description | Type |
+|--------|-------------|------|
+| error | Error message if encoding fails | str |
+| encoded_text | The encoded text with special characters converted to escape sequences | str |
+
+### Possible use case
+<!-- MANUAL: use_case -->
+**JSON Payload Preparation**: Encode multiline or quoted text before embedding it in JSON string fields to ensure proper escaping.
+
+**Config/ENV Generation**: Convert template text into escaped strings for `.env` or YAML values that require special character handling.
+
+**Snapshot Fixtures**: Produce stable escaped strings for golden files or API tests where consistent text representation is needed.
+<!-- END MANUAL -->
+
+---
+
 ## Text Replace
 
 ### What it is