Enables Fava integration for entry management

Adds functionality to interact with Fava for managing
Beancount entries, including fetching, updating, and
deleting entries directly from the Beancount ledger.

This allows for approving/rejecting pending entries
via the API by modifying the source file through Fava.

The changes include:
- Adds methods to the Fava client for fetching all journal
  entries, retrieving entry context (source and hash),
  updating the entry source, and deleting entries.
- Updates the pending entries API to use the Fava journal
  endpoint instead of querying transactions.
- Implements entry approval and rejection using the new
  Fava client methods to modify the underlying Beancount file.

fava_client.py

@@ -525,6 +525,149 @@ class FavaClient:
             limit=limit
         )
 
+    async def get_journal_entries(self) -> List[Dict[str, Any]]:
+        """
+        Get all journal entries from Fava (with entry hashes).
+
+        Returns:
+            List of all entries (transactions, opens, closes, etc.) with entry_hash field.
+
+        Example:
+            entries = await fava.get_journal_entries()
+            # Each entry has: entry_hash, date, flag, narration, tags, links, etc.
+        """
+        try:
+            async with httpx.AsyncClient(timeout=self.timeout) as client:
+                response = await client.get(f"{self.base_url}/journal")
+                response.raise_for_status()
+                result = response.json()
+                return result.get("data", [])
+
+        except httpx.HTTPStatusError as e:
+            logger.error(f"Fava journal error: {e.response.status_code} - {e.response.text}")
+            raise
+        except httpx.RequestError as e:
+            logger.error(f"Fava connection error: {e}")
+            raise
+
+    async def get_entry_context(self, entry_hash: str) -> Dict[str, Any]:
+        """
+        Get entry context including source text and sha256sum.
+
+        Args:
+            entry_hash: Entry hash from get_journal_entries()
+
+        Returns:
+            {
+                "entry": {...},  # Serialized entry
+                "slice": "2025-01-15 ! \"Description\"...",  # Beancount source text
+                "sha256sum": "abc123...",  # For concurrency control
+                "balances_before": {...},
+                "balances_after": {...}
+            }
+
+        Example:
+            context = await fava.get_entry_context("abc123")
+            source = context["slice"]
+            sha256sum = context["sha256sum"]
+        """
+        try:
+            async with httpx.AsyncClient(timeout=self.timeout) as client:
+                response = await client.get(
+                    f"{self.base_url}/context",
+                    params={"entry_hash": entry_hash}
+                )
+                response.raise_for_status()
+                result = response.json()
+                return result.get("data", {})
+
+        except httpx.HTTPStatusError as e:
+            logger.error(f"Fava context error: {e.response.status_code} - {e.response.text}")
+            raise
+        except httpx.RequestError as e:
+            logger.error(f"Fava connection error: {e}")
+            raise
+
+    async def update_entry_source(self, entry_hash: str, new_source: str, sha256sum: str) -> str:
+        """
+        Update an entry's source text (e.g., change flag from ! to *).
+
+        Args:
+            entry_hash: Entry hash
+            new_source: Modified Beancount source text
+            sha256sum: Current sha256sum from get_entry_context() for concurrency control
+
+        Returns:
+            New sha256sum after update
+
+        Example:
+            # Get context
+            context = await fava.get_entry_context("abc123")
+            source = context["slice"]
+            sha256 = context["sha256sum"]
+
+            # Change flag
+            new_source = source.replace("2025-01-15 !", "2025-01-15 *")
+
+            # Update
+            new_sha256 = await fava.update_entry_source("abc123", new_source, sha256)
+        """
+        try:
+            async with httpx.AsyncClient(timeout=self.timeout) as client:
+                response = await client.put(
+                    f"{self.base_url}/source_slice",
+                    json={
+                        "entry_hash": entry_hash,
+                        "source": new_source,
+                        "sha256sum": sha256sum
+                    }
+                )
+                response.raise_for_status()
+                result = response.json()
+                return result.get("data", "")
+
+        except httpx.HTTPStatusError as e:
+            logger.error(f"Fava update error: {e.response.status_code} - {e.response.text}")
+            raise
+        except httpx.RequestError as e:
+            logger.error(f"Fava connection error: {e}")
+            raise
+
+    async def delete_entry(self, entry_hash: str, sha256sum: str) -> str:
+        """
+        Delete an entry from the Beancount file.
+
+        Args:
+            entry_hash: Entry hash
+            sha256sum: Current sha256sum for concurrency control
+
+        Returns:
+            Success message
+
+        Example:
+            context = await fava.get_entry_context("abc123")
+            await fava.delete_entry("abc123", context["sha256sum"])
+        """
+        try:
+            async with httpx.AsyncClient(timeout=self.timeout) as client:
+                response = await client.delete(
+                    f"{self.base_url}/source_slice",
+                    json={
+                        "entry_hash": entry_hash,
+                        "sha256sum": sha256sum
+                    }
+                )
+                response.raise_for_status()
+                result = response.json()
+                return result.get("data", "")
+
+        except httpx.HTTPStatusError as e:
+            logger.error(f"Fava delete error: {e.response.status_code} - {e.response.text}")
+            raise
+        except httpx.RequestError as e:
+            logger.error(f"Fava connection error: {e}")
+            raise
+
 
 # Singleton instance (configured from settings)
 _fava_client: Optional[FavaClient] = None